A Review on Sustainability Characteristics Development for Wooden Furniture Design

Abstract

The design of furniture products is influenced by increasing consumer interest in green products and sustainability values. However, although the demand for sustainable furniture products is high, the standardization of sustainability characteristics in furniture design has still not been achieved. A thorough literature review was conducted, which considered various sustainability characteristics that apply in industries that design furniture. This review paper aimed to identify common sustainability characteristics so that a new standard for furniture industries can be established. In this review, numerous themes were explored relating to design guidelines, design criteria, design preferences, design optimization, design evaluation and assessment, design decision making, strategic planning, design strategies, the integration of eco-design, and eco-design tools. A total of 137 articles were reviewed regarding their sustainability characteristics according to the triple bottom-line framework for a relevant product sector. Due to the limited reports on the sustainability characteristics of furniture design activities, this paper also tried to include common sustainability characteristics of non-furniture products that are available on the market. Through the review, 10 sustainability characteristics were identified for the environment, 17 for the economy, and 16 for the social dimension as being common among manufacturers when designing their products. A further in-depth analysis was conducted by mapping the characteristics to those that were significantly implemented in the design process, of which five (5) were environmental, two (2) were economic, and five (5) were social sustainability characteristics. This review is significant in helping furniture designers to use appropriate and effective sustainability standards in the design and manufacture of products that meet customers’ demands. Previous literature reviews have not clearly measured the triple bottom line. Furthermore, no definite characteristics were proposed in previous works regarding wooden furniture design, leaving a gap to be closed by future works.

1. Introduction

Wood is one of the materials used in global furniture production and is mainly used in southeast Asian countries [1,2,3,4]. The value of global furniture exports, excluding seats and medical, surgical, dental, or veterinary furniture, from 2015 to 2021, amounted to more than USD 630.4 billion [5]. Further classifications have been made for wood-based furniture production [1], and the data obtained from export value statistics, which include information on wooden furniture for bedrooms, kitchens, offices, and other uses [5], show that the industry is worth USD 345.3 billion. In 2015, global trade in furniture based on these four types was valued at USD 45.8 billion and slightly increased to USD 60.5 billion in 2021. China dominated the market worldwide, with exports of the four types of wooden furniture products worth USD 93.8 billion. Export values the four types of wooden furniture for the the ten global largest exporters from 2015 to 2021 are shown in Figure A1.

It was anticipated that the global furniture market’s export values would grow by 12% in the next five years [6], with Asian countries set to lead as producers of furniture [7]. One of the current competitive furniture exporters is Malaysia; however, it has yet to actively focus on sustainability characteristics [8]. Western European countries, meanwhile, are leaders in new designs, environmental approaches, sustainable natural materials, high-value-added furniture production, and new technology [7].

In 2019, the International Trade Centre (ITC) [9] reported a 92% increase in the sales of sustainable products by furniture retailers. The sale of home and office furniture products, which is expected to increase by 96% over the next five years, was one of the key product categories that was highlighted.

Previous studies have emphasized how sustainability consciousness in the wooden furniture industry is essential to reduce the 10 million tonnes of furniture that is discarded to landfill each year [1,2,10,11,12,13,14]. As a result, sustainability has become a trend in design decisions, including those in wood-based industries [1]. The previous literature reviews have shown no definite standard in the employment of sustainable characteristics in furniture industries according to the triple bottom-line framework. Therefore, this study aims to deconstruct the concept of “sustainability” in wooden furniture design and assign guidelines for the decomposed features. The “triple bottom line” model was used for the decomposition, while the requirements for the features were developed based on the reviewed literature.

2. Rationale of the Study

Sustainability issues and related challenges in furniture industries have emerged at two stages, namely, manufacturing [15,16,17,18] and the end-product stage [2,15,19,20]. As a result, sustainability issues affect both workers (during the furniture-making process) and users [21]. This study will focus on the end-product stage instead of the manufacturing process, as control and management must begin at the early design stage to achieve sustainability in manufacturing and, ultimately, in the end products [22,23,24,25,26].

The focus on sustainable design, practise, process/methodology, and certification in furniture design is insufficient throughout the product development process (PDP) [15]. It overlooks novel methods or design concepts that are tailored to the characteristics of furniture design that will entice architects and designers to produce creative and sustainable furniture designs to satisfy future demands [15,27]. Designers are seldom exposed to sustainability considerations at the early design stage, which affect product cost and lead to unsustainable products being produced for users [28,29]. Consequently, most new furniture designs and prototypes fail to reach successful standards. Furniture designers lack the encouragement to express their ideas and designs [27]. Performance, cost, aesthetics, and product standardization will be limited if sustainable design is not deployed in the industry [30], and designers will not be able to impact the environment and society with their products [31].

Therefore, this paper explores sustainability characteristics according to the triple bottom-line of environmental, economic, and social factors to implement in furniture design in the Malaysian context. Hence, a tool will be developed based on the identified sustainability characteristics to assist designers in assessing their current furniture designs and enhance sustainable furniture design throughout the product development process (PDP). This effort is made to ensure that Malaysian furniture designers can reinforce marketability. This will encourage the company to perceive market opportunities and become sustainability leaders in furniture development [32]. In addition, it intensifies the consumer’s acceptance and recognition of sustainable furniture [33] and the innovative abilities of the Malaysian furniture industry [18].

3. Literature Review

The literature on global furniture relating to wooden furniture and sustainability issues is reviewed and discussed in this section. The term “sustainability” is clarified by by the epistemological standpoints of sustainability, triple bottom line, wooden species, furniture structural strength, and the related integration approach, specifically in the early stages of product design. The later section presents and discusses previous works focusing on eleven themes derived from the previous literature. At the end of this discussion, the sustainability phenomenon design was identified and proposal was made to fill any research gaps in the integration approach to be used in the design of wooden furniture.

Timber is one of the main materials used to make furniture in Malaysia, and its sustainability is necessary for this sector [2]. However, substantial environmental factors are a necessary concern to ensure the success of the furniture industry [32]. The ecological situation for furniture manufacturing is also highlighted, impacting emissions such as noise, air, water, and waste generation [21]. The Malaysian furniture industry is under pressure to comply with sustainability regulations and policies to increase marketability as a result of this issue [15].

3.1. Wood Species in Furniture Industries

Apart from the noticeable awareness of the environmental effects of the wood-making furniture industries, another important consideration is sustainable wood selection. The selection is significant in sustaining furniture design, indirectly affecting user perception of the end products [1].

Since wood is a reputable material in the furniture industry, it provides various benefits, such as renewable resources, regenerative fuel, a pleasant, beautiful appearance, high insulation capacity, low weight, and ability to mitigate climate change by acting as a carbon sink [34]. Wood species is a primary consideration when determining suitability for furniture production. Generally, there are two sources of wood species in Malaysia. First, the local supply that provides a variety of hardwood species, such as Rubberwood, Meranti, Kempas, Merbau, And Merapuh. Secondly, the exported hardwood species, which consist of Poplar, Oak, and Cherry. The raw material sustainability will influence the choice of timber species utilised in wood-based production [35].

Apart from conventional woods, there is also an alternative material used in furniture production. Many studies have identified materials formed by reinforced fiber from agricultural waste, biomaterial, recycled plastics, and post-consumer waste [36,37,38,39,40,41]. Due to its sustainability, alternative material will improve product use and lifespan and enhance designers’ understanding of the utilisation of sustainable material for furniture [1].

3.2. Furniture’s Structural Strengths and Durations

Another important aspect of furniture design the furniture’s strength and durability over time. Furniture production focuses on assembly techniques involving connectors, fasteners, and adhesives; these should also consider sustainability. For example, a typical connector is widely used in structural assembly in furniture production. For instance, dowel must be massively produced with high quality to specific forces [42]. Another technique used when assembling the structure of wooden furniture is adhesives, whether made from synthetic or natural materials. Therefore, the study was conducted to test the adhesives’ suitability and durability, ensuring that no harm is posed to the environment or to people [43]. In addition, some studies looked into sustainability in relation to the connectors, fasteners, and adhesives used in the manufacture of wooden furniture, such as VOC pollution [44] and carbon emission [45]. Another important consideration is the strength and durability when two different types of woods are joined together. The analysis is significant in ensuring the versatility of designs from the furniture-making perspective [46]. Therefore, the joining system must always be considered to ensure that the lifespan of the design structure can be maintained.

3.3. Sustainability Integration in Designing Furnitures

Organizations must consider the importance of integrating sustainability into the product development process [47,48]. Genç and Di Benedetto [49] highlighted that integration offers many benefits for businesses, such as reducing manufacturing inefficiencies and producing cost benefits. Lacasa et al. [50] stated that, to create a good and high-quality product while lowering costs, competitive organisations incorporate sustainability into their product development process. Other scholars have mentioned that the integration strategy would help designers to create sustainable products that are both economical and environmentally friendly [51,52,53].

To understand the integration of sustainability into the product development process, a review of the 50 articles was conducted, as summarized in

Table A1. Sustainability Integration Theme.

No.	Theme	No. of Study
1	Design Guideline	2 [54,55]
2	Design Process	15 [23,28,29,30,56,57,58,59,60,61,62,63,64,65,66]
3	Design Criteria	3 [31,67,68]
4	Design Preferences	1 [69]
5	Design Optimization by Simulation Model	7 [70,71,72,73,74,75,76]
6	Design Evaluation and Assessment	7 [77,78,79,80,81,82,83]
7	Design Decision	1 [84]
8	Strategic Planning	6 [25,85,86,87,88,89]
9	Design Strategies	5 [32,90,91,92,93]
10	Integration of Eco-Design	2 [94,95]
11	Eco-Design Tool	1 [96]
Total		50

(in Appendix A). The integration concept was determined and analyzed according to the respective themes and related studies. Details on each theme, summaries of previous studies and an identification of the study’s consideration, including the framework, methods, tools, steps, and characteristics that could be implemented and improvised to further develop and enhance of the body of knowledge, can be seen in Table A1.

3.3.1. Design Guideline

A design guideline is a set of specific recommendations that usually implement design principles to allow for designers to meet user needs. This theme provides two related studies that clarify the design guidelines in the early design stage.

Corsini and Moultrie [54] provided a framework to guide designers in the evaluation of products emphasizing digital fabrication. The authors discussed how the early stage of the design process could help designers influence the degree to which products must start with social sustainability. However, this study ignored the circular economy factor and only examined how the entire product’s social effects were affected by digital fabrication.

Baeriswyl and Eppinger [55] established guidelines and implemented a design for environment (DFE) strategy through teaching methods selected by the design team, which were implemented in the early design stages. The study focused on the closed-loop lifecycle system using the qualitative assessment method and practical design guidelines. However, the DFE method was only geared towards environmental awareness and did not have an economic and social impact on product development.

In can be seen that both works developed a framework related to the design guideline through the design stage, but did not fully employ the characteristics of the entire triple bottom line, which are listed accordingly.

3.3.2. Design Process

A design process is a design activity that implements various methods based on a particular problem to generate the design requirements. This theme provides 15 related studies that defined the design process in the early design stage.

In 2019, Shen et al. [28] developed a Design merge X (DMX)-related framework; a combination of industrial design and product design with the conventional design for X (DFX) method. The approach aimed to help designers evaluate the entire design in the early design stage to prevent rework and design changes. Nevertheless, this neglected the circular economy factor and social aspects.

In the same year, Rossi et al. [30] developed an approach to consolidate various analyses of the conventional product development process. This study identified the drivers’ checklist based on the literature review. This approach aimed to test its capabilities by conducting two case studies and analyze the environmental factors using LCA Software SimaPro 7 and EcoInvent v 2.2. However, the social dimension was not defined, since the research only focused on eco-design products.

Another interesting work was conducted by Alli and Sazwan Mohd Rashid [29], who developed a method called the Sustainable Product Design Method (SPDM), which consists of three evaluated variables. Thirty-seven elements were identified and tested to analyse the emotional responses and perceptions that emphasise user satisfaction, aesthetics, function, quality product, and sustainable design. All these elements were essential in assisting designers in generating a concept idea for a sustainable product. Although the method was wonderfully developed, they did not fully emphasise the triple bottom line of the sustainability element.

In another study, Luz et al. [56] suggested integrating the LCA method into the product development process (PDP), which consists of three macro-phases. The purpose of this integration was to assist decision-makers in the selection of an alternative to environmental performance to improve the product. However, although the research emphasised the environmental element applied to this method, it did not consider the economic and social factors and only described them for future research.

Similarly, Buchert et al. [23] developed a system based on information technology (IT), namely, Design Decision Support Assistant (DDSA), which aimed to support the sustainable product development processes by adopting a repository containing 29 sustainable product development methods. It is interesting to note that this bundle of methods will affect its maturity in research testing. It is complicated in its industrial setup, requiring the designer to study new approaches as time passes.

Fernandes et al. [57] proposed integrating the sustainability-oriented method of product development, especially in the concept design phase, with the implementation of design recommendations. Integrated Product Development (PDI) is a sustainability orientation developed for information and concept design, in which designers interpret the generation of ideas. At the end of the study, the method was found to be practical in the design process for any product category. The study also did not recognize sustainability characteristics following the triple bottom line.

Mokhtar et al. [58] developed a framework to integrate sustainability factors in the supply chain management into the design phase of the product development process. This aims to support designers and engineers during the design phase using a score metric measurement method to predict, evaluate, and optimise the product design, sustainability, and supply chain in product development. Only a small number focused on the integration of the supply chain with the product development process, which can be assessed by the designers.

Papahristou and Bilalis [59] developed a new model based on corporate social responsibility (CSR) and the Collective Action on Sustainability theory by integrating the design processes that were aligned with new 3D virtual simulation and 3D prototyping technology. The purpose of CSR was to unify customer values in product development, to fulfil the target market and achieve company objectives regarding sustainability. However, this model only emphasized the ecological factors and did not elaborate on how economic and social factors can influence sustainable product development.

Similarly, Pacelli et al. [60] proposed a new design method, using industrial scrap materials to guide designers in the production of product designs based on industrial scraps/waste in the early design stage. This effort aimed to address the value of the economy and the environmental issues. The approach consisted of three steps to facilitate designers to identify the scraps used in the product design process. However, the proposed method did not provide a list of the triple bottom line to maximise sustainability.

Furthermore, Moreira et al. [61] proposed a novel, sustainable, product development framework to communicate between the process, supplier, and consumer and emphasized sustainable features that cover the entire process of three macro-phases. The additional stress factors were waste and supply chain management, which were linked to each stage of the product development process. However, the study did not detail the triple bottom line’s sustainability component because its primary goal was to create a new framework for the product development process.

Rossi et al. [62] suggested a new method to implement the eco-design strategy by integrating Ecodesign guidelines and company eco-knowledge into the product development process (PDP). The integration approach can assist the designer in adopting the Case-Based Reasoning (CBR) approach to decision making and identifying initial design selections that meet the sustainability characteristics, to minimize the environmental impacts and improve the lifecycle product in the early design phase. However, the method only focused on the environmental impact and did not emphasise the triple bottom line in the study.

Another work, reported by Carulli et al. [63], proposed a method of identifying consumer needs based on virtual reality technology (VR). This approach is commonly used in the early design phase to minimise production costs and can change the customer’s voice to improve the design of mass-customised products. The technology system was indeed expensive and time-consuming, especially during the design process. Additionally, the study’s integration of sustainability into PDP was not discussed, especially its position in the framework.

Flores-Caldero’n et al. [64] synthesized Datschefski’s Total Beauty theoretical framework, which contained five sustainability criteria to improve the percentage of sustainability in product design. However, the study only assessed the material attributes of product design and did not focus on any specific characteristics according to the triple bottom line.

Gotzsch [65] suggested that the product attraction model acknowledges the characteristics of eco-design practice as an integration approach for the sustainability element in sustainable product creation. The model would help small and medium-sized companies to perform eco-design and innovation practices in the production of sustainable products. However, this study only focused on ecological perception, with no emphasis on the economic and social factors. In addition, the integration of this model into the product development process was not reflected, although the practice was appropriate in the early design stages.

Großmann et al. [66] presented the methods and approaches to enhancing the technical, economical, and environmental aspects of the product development process using the Integrated Product and Process Development (IPPD) method. The method supported and assisted mechanical engineers, industrial designers, and manufacturers in identifying and developing ideas and design solutions to obtain quality sustainable products in the early design stage. The methods employed in the product development process did not, in fact, create a distinct classification for each sustainability component.

Overall, it can be inferred from the review that, despite the framework’s connection to the design process throughout the design stage, no prior research reported on the consistent application of the triple bottom line’s characteristics. Only one study integrated the supply chain into the triple bottom line, and none of the papers provided clear definitions of the economic and social characteristics.

3.3.3. Design Criteria

A design criterion is a clear goal that a project must meet to succeed. Thus, three related studies that have defined design criteria in the early design stage are discussed under this theme.

Kuo and Wang [31] identified and verified a set of design criteria, reviewed by the Robust Design Criteria and Axiomatic Design Principles, to support Sustainable Product Development and help designers select appropriate criteria to produce and improve a sustainable product. However, this study did not explore every process involved in product development. Furthermore, the study emphasized the sustainable aspects of product design but did not explicitly discuss how to evaluate or collect data on environmental dimensions. There was no further deliberation on the cost or profit of design improvement, or the social aspects.

Mesa et al. [67] established a set of criteria for measuring the sustainability performance of certain family products and considering the circular economy. The criteria identified six indicators based on a literature review of conventional sustainability measurements, existing circular economy indicators, and product family attributes to measure the performance of family products. However, the study did not identify these criteria according to the triple bottom line, making it difficult to assess the social elements.

Hassan et al. [68] used sustainability criteria to determine the sustainability performance of evaluated products using the weightage of sustainability metrics to finalise the design configuration. This would help product designers to choose various designs at the early stages of the design concept. The assessment implemented 46 sets of criteria in relation to the three sustainability elements. Although this proposal highlighted the three sustainability assessment components, which include 46 criteria, it does not detail how each sub-criteria and evaluated weighting affect the product development framework.

Therefore, it can be concluded from the above review that the proposed framework is related to design criteria throughout the design stage, but neglects the significance of the triple bottom line.

3.3.4. Design Preference

A design preference is a variety of attributes that are implemented into the different processes. Thus, one related study that defined design preferences in the early design stage will be discussed under this theme.

Inoue et al. [69] developed the Preference Set-based Design (PSD) method for various structures and materials and integrated it into the ecological dimension of sustainability to support decision-making activities. It was measured based on the designer’s experience with the design-solution objectives and then evaluated based on the sustainability indicator for design performance in the early design phase.

Consequently, the study listed these characteristics according to the triple bottom line, aiming to obtain a design preference; however, further clarification and selection need to be considered in this study. Furthermore, the study did not provide details of the social impact, as this is difficult to measure and requires much research on the social dimension. In addition, the study did not consider the exchange of information or product requirements at any product development stage. Still, it remains a good strategy even though it only focused on the early stages of the design.

3.3.5. Design Optimization

Design optimization is an engineering approach that uses a mathematical formulation of a solution problem to aid in the selection of the best design from a variety of options. Thus, seven related studies that defined the design optimization in the early design stage are discussed under this theme.

Ameli et al. [70] aimed to help producers make their product decisions by optimising design and EOL. The study focused on the creation of valuable models to evaluate a sustainable product performance, covering its environmental, economic, and social impacts. The study suggested including this approach in the assessment of circular economy strategies. However, the study proposed complex parameters, particularly for designers.

Another exciting work was conducted by Hapuwatte and Jawahir [71], who led a preliminary study on the development of a framework that integrates a predictive model and Total Life Cycle (TLC) to help designers identify and promote product performance and improve sustainability at the product design stage. However, the study did not highlight the sustainability characteristics regarding the triple bottom line, and most of the sustainability concerns were converted into metrics.

It is also interesting that De Paula and Rozenfeld [72] focused on Mass Properties Management (MPM), which requires information data for the early design concept stages. These data must be accurate, as they are used for design optimisation decisions. However, the study did not clearly explain how sustainability could be integrated into this framework, and the characteristics of the triple bottom line were also not highlighted.

In another study, Eigner et al. [73] developed a framework for the creation of product system modelling during the initial design phase, considering hte sustainability aspects to solve problems in the sustainable product development process. However, the framework omitted the precise location of sustainability to guarantee that stakeholders, particularly designers and engineers, understood this and could incorporate it into the product development process. It did not list characteristics according to the triple bottom line and was limited to the environmental dimension.

Eigner et al. [74] proposed building a concept based on Product Lifecycle Management (PLM), which would be integrated with Sustainable Product Lifecycle Triangle to manage the overall product life cycle data and monitor sustainable product development at an early design phase. However, this system places too much emphasis on the use of scientific knowledge in design, making the use of this approach to create sustainable products too complex. A detailed discussion of the sustainability triangle’s indicators was also omitted.

To address the manufacturing costs identified during the embodiment design and to consider product quality, Hoffenson et al. [75] concentrated on dimensional tolerance in the product development process. The developed model assists companies in producing diverse and different product attributes based on price, environmental impact, and high product quality. However, the authors did not extensively highlight the characteristics of the developed model.

On the other hand, Leibrecht et al. [76] established an information framework by integrating the Life Cycle Analysis (LCA) and Computer-Aided Design (CAD), and were assisted by experts in identifying the best design solution in the product development process, considering the sustainability factors that were applied by engineers. However, this study only focused on environmental elements; the economic and social factors were not described in detail. This model is also not suitable for use by designers, who are responsible for design attributes at early stages of the product development process.

In summary, the triple-bottom-line characteristics were not explicitly defined in previous works; therefore, a new approach to design optimization is needed at the design stage. The reviews did not focus on a specific stage of the product development, and certain reports showed a complex method, which should be used as a guideline.

3.3.6. Design Evaluation and Assessment

The process of collecting data and analysing the application of new or existing approaches by offering feedback on the process is known as design evaluation and assessment. To define design evaluation and assessment in the early design stage, this theme presents seven related studies.

Raoufi et al. [77] developed a set of questionnaires to allow for non-engineering experts to select various commercial sustainability tools and methods to determine the most appropriate approach to sustainable product evaluation. The study aimed to assist designers in choosing the right tools or methods to analyze sustainable product designs. However, the software lacks an analysis of social responsibility indicators and no visual comparison was made between the appearance of the initial design and improved design. Furthermore, there was no expert judgment and opinion on the proposed design improvement, based on the data. The use of tools and methods by which a non-expert could perform a sustainable product analysis for final design selection were not highlighted.

Turan et al. [78] developed a new method to evaluate the design concept by integrating the fuzzy-technique and sustainability. The approach used the “weighing scale” and “criteria-based” techniques to analyze data that could help designers and engineers to further strengthen their sustainable product development and measure design performance. However, the sustainability criteria were not strong enough to explain the developed framework applications, which were primarily based on three sustainability elements.

Simões et al. [79] developed a framework that integrates the Life Cycle Assessment and Life Cycle Cost (LCA/LCC) model based on the ISO14040 series methodology. This considers the economic and environmental aspects, which are reasonably practical for a designer selecting appropriate materials at the beginning of the design process. However, the study did not provide detailed design parameters or requirements for material selection. The social impact was also not detailed in the developed framework.

Panarotto and Törlind [80] developed a matrix analysis framework, namely, the Sustainability Innovation Workshop (SIW), based on analyzing existing eco-tools in the literature to identify essential characteristics. The characteristics aim to assist in the development of an easy-to-use SIW method that supports sustainability innovation at an early design stage. However, although these tools focused on the early design stage and identified sustainability challenges, three sustainability elements were not emphasised in the developed framework.

Donnelly et al. [81] developed a framework, the Product-Based Environmental Management System (PBEMS), using the Design for Environment (DfE) and Life Cycle Assessment (LCA) approach. The framework system implements environmental management through sustainable development, especially in the early design stage, to improve product quality. However, this framework did not address the economic and social factors of the development process.

Persson [82] suggested that the integration of an eco-indicator into product development was emphasised in the early design stages and implemented in the finished products. An appropriate eco-indicator is recognized to assist in the design of sustainable products. However, the study only identified indicators based on their environmental aspects. It did not analyse the economic and social elements that determine its characteristics.

Veroutis and Fava [83] developed a decision-making tool to support the design for environment (DFE) Criteria Mapping Matrix, using a qualitative approach to assist designers in assessing the environmental and product design based on five (5) environmental criteria and the product life cycle. However, it may not be possible or designers to use this metric, due to the lack of suitable, available data. Besides, the study only focused on the environmental factors of the product development process and did not discuss economic and social factors in any detail.

In conclusion, the above studies suggested a method for implementing design evaluation and assessment into the design stage. However, in their studies, the triple bottom line was only evaluated using a simple metric approach and software. Additionally, the economic and social aspects of the triple bottom line were not adequately addressed.

3.3.7. Design Decision

The solution to this problem is determined by the design decision, which is based on the strategies that are chosen to ensure an effective design. Thus, one related study that defined the design decision in the early design stage will be discussed under this theme. Ahmed et al. [84] developed a product development system to help designers decide on the products that they will produce. The approach comprises three modules, each consisting of four basic Sets of Experience (SOE), for better decision-making. SOE assists designers and engineers in selecting materials, parameters, tooling, machining, and new equipment. Although the study established a new method for the design decision during the design stage, the triple-bottom-line characteristics are not adequately listed. In addition, the study did not address the economic and social factors but only discussed issues related to sustainability material and the manufacturing process.

3.3.8. Strategic Planning

Strategic planning is the process of collecting information and determining a direction for the project to follow so that it attains its objectives. Thus, six related studies that defined strategic planning at the early design stage are discussed under this theme.

Teixeira and Junior [85] discussed the company’s performance in changing business management by implementing strategic plans and continuous improvements using the Planning of the Integrated Process for the Development of Sustainable Products (PEPDIPS) method. This comprises five (5) sets of parameters with specific elements to determine the company management’s maturity and verify any improvements in product development. In their study, sustainability characteristics are defined through a parameter, element, or variable that can be changed according to the case. However, the study did not specifically focus on the design phase.

De Medeiros et al. [25] suggested a reference system that could manage the green product development process (GPDP) to examine the relationship between sustainability, product development and collaboration practice in small and medium-sized enterprises producing new green products. However, while the study suggested a green product development process, looking at the environmental impact, it did not focus on the social dimension.

Teixeira and Junior [86] developed a conceptual method for the Strategic Planning of the Integrated Sustainable Products Development Process (PEPDIPS) as a guide to the Product Development Process (PDP) by strategising an action plan of sustainability issues to produce sustainable products. However, the focus of the work was not on the integration of the three sustainability pillars into the development process, particularly regarding the social component.

Pitta and Pitta [87] established a strategic canvas that integrated the New Product Development (NPD) process to reduce the failure rate and create a more competitive product. The study suggested a four-action plan approach and adopted the six paths framework to help product developers provide a competitive market and increase new products. However, the study did not discuss the sustainability element in detail, and integration into the product development process was not addressed. The study also did not disclose the actor who would use the method in the organisation.

Ny et al. [88] developed Design for Sustainability (DfS) models that integrated the Method for Sustainable Product Development (MSPD) with Templates for Sustainable Product Development (TSPD). The support tool aims to assist and facilitate the product design team and sustainability experts to solve the sustainability challenges and product categories at the early design stage, using a qualitative method without neglecting the triple bottom line. However, the instrument’s use levels weres low and the product was not verified. Thus, it was difficult for the design team to understand the proposed approach. This approach did not fully utilize the design changes to ensure sustainability.

Kara et al. [89] developed a sustainability integration framework for sustainable product development (SPD) that focused on the environmental consideration of manufacturing companies by establishing three organization levels and several control factors at the early design stage. However, the proposed framework does not describe its position during the product development process, although it was implemented in the early design stage. The framework emphasised the environmental factor but did not discretely explain each sustainability element, especially the economic and social aspects.

Overall, the above review began a strategic planning phase for the entire product development process, but did not pay attention to the design phase. Thus, it is necessary to incorporate the triple bottom line’s characteristics into strategic planning.

3.3.9. Design Strategies

The design strategies extend the tactics and strategy of project planning to the user’s need to build a successful product. This theme provides five related studies that defined design decisions at the early design stage.

Mesa et al. [90] evaluated the modularity concept in product development, especially regarding sustainability issues. The Modular Architecture Principles (MAPs) aimed to identify the product lifecycle in the early design stage by suggesting five (5) key design strategies. This aims to increase the sustainability associated with modular architecture principles and cannot be used in other types of modular design. However, the study did not address the sustainability aspect in a manner that was consistent with the triple bottom line.

Kaspar and Vielhaber [91] studied innovative lightweight designs to achieve sustainability in the product development process (PDP) with the primary objective of reducing the size and space of the component, and the assembly process. Furthermore, a framework was developed for an integrated, cross-component, lightweight, and material-oriented design (LMOD). However, the study did not show that the optimal process can communicate with design strategies and did not fully describe the social sustainability of the design process.

Fernandes and Canciglieri [92] developed a conceptual model by integrating sustainability into a sustainable development process, emphasizing the design concept to assist designers in the production of alternative design concepts based on sustainability and the product life cycle. However, designers lack the technical knowledge of material information, production process, design for environment (DFE), and new technologies, which are to implement the model for sustainable products. In addition, economic and social factors were not discussed, which would integrate the three significant pillars of sustainability.

Dangelico et al. [32] developed a framework based on external abilities being integrated into the development of new products to create new opportunities and improve the company’s financial performance. Therefore, the study’s primary purpose was to investigate the external collaboration network, as this is vital in integrating environmental issues regarding the product design and manufacturing processes. However, the study did not explain the three critical sustainability factors, and its integration into the product development process was not displayed in the framework.

Tingström et al. [93] discussed a sustainable model, which integrates product development into the sustainability project. The study showed that integrating sustainability could help the company to improve its product development and environmental performance. However, the study did not clearly explain and include social sustainability in the early design phase and did not show how it was implemented into the process.

In sum, it should be noted that this discussion did not list characteristics in accordance with the triple bottom line but instead concentrated on the integration of design strategies into the entire process, directed toward the design stage. Additionally, the social and economic aspects were not clearly defined.

3.3.10. Integration of Ecodesign

Ecodesign integration is a way of obtaining essential data on the lifecycle process, including product geometry and material inventory, and integrating them into product development. Two related studies that have defined the integration of ecodesign into the early design stage are discussed under this theme.

Brones and Monteiro De Carvalho [94] developed a framework for the integration of eco-design into the product development process, based on 52 integration models, to identify and analyze the management’s knowledge of ecodesign. This aimed to assist the company’s management in improving product design by implementing ecodesigns and integrating the sustainability element into project management. However, the study did not review the specific sustainability characteristics based on the triple bottom line, which was implemented throughout the framework.

May et al. [95] studied the integrated sustainable framework that is used to design products, focusing on the environmental factors, and aimed to identify how the company used this approach in design process activities. The study also developed an understanding of the use of existing eco-design tools to support sustainability in the early design stage. However, it was found that companies failed to implement sustainability in product development process activities because the current tools are unsuitable for the designer. In addition, companies neglect sustainability in the early design phase, and the process is time-consuming and costly. Furthermore, the sustainability considerations were not mature enough. The study did not clearly illustrate how the sustainable framework is integrated into the product development process, particularly the early design phase.

The preceding discussion proposed integrating the eco-design focus into the entire product development process without using a specific design process. However, these study did not list characteristics according to the triple bottom line, which left a gap in the research.

3.3.11. Ecodesign Tool

An ecodesign tool is a tool for the designer to identify the product life cycle’s influence on the environment by providing effective measures to improve product performance. Thus, one related study that defined the ecodesign tool in the early design stage is discussed under this theme.

Germani et al. [96] studied the development of web-based, eco-design tools named G.EN.ESI. These provided an approach to software’s integration into the product development process to support the decision-making process in creating sustainable products that can be implemented at the early design stage. Thus, it could help designers to analyze eco-design and implement eco-innovations to choose the best design solution.

The study was conducted using eco-design, web-based tools related to the design stage; however, the sustainability characteristic does not comply with the triple bottom line. Moreover, these characteristics may differ, such as the criteria, company objectives, and product development. The designer had no prior tool-use experience, which increased the amount of training that was required. Designers may also lack knowledge of the principles of the method and have less skill in using the software, and the complexity of the approach is hard to comprehend. Although LCA can identify sustainability factors, this approach, particularly in the developed framework, did not elaborate on the three elements of sustainability.

4. Summary of Previous Works

This section summarizes a review of 50 previous articles according to eleven themes related to the integration of sustainability into early product design. The research gap was also determined based on the previous study, which aimed to improve or develop new approaches.

In conclusion, the identification of characteristics based on the triple bottom line (environment, economic, and social) was based on the results of previous research.

Table A2. Summaries of previous studies based on a related theme.

No.	Author and Year	Theme	Aim/Objective/Focus	Integration Framework in PDP	Findings	Research Gaps
1.	Corsini and Moultrie (2019) [54]	Design Guideline	Guidelines for social sustainability design during the digital fabrication of a humanitarian project.	Yes	DfSS Framework	(i) Directly toward the design stage. (ii) No characteristics listed according to TBL.
2.	Baeriswyl and Eppinger (2011) [55]		Teaching design for environment (DFE)	Yes	Teaching method	(i) Directly towards the design stage. (ii) No characteristics listed according to TBL.
3.	Shen et al. (2019) [28]	Design Process	DFX and Design Method	Yes	Design Merged X (DMX) framework	(i) Directly toward the design stage. (ii) Not listing characteristic according to TBL.
4.	Rossi et al. (2019) [30]		Multi-criteria Index	Yes	Design solution	(i) Directly toward the design stage. (ii) Social dimension was not defined, since the research focused on eco-design.
.5.	Buchert et al. (2017) [23]		Selection SPD tools and method	Yes	IT system	(i) Directly toward the design stage. (ii) No characteristics listed according to TBL.
6.	Luz et al. (2018) [56]		LCA integration in PDP	Yes	Product optimization	(i) LCA identified the entire process. (ii) Economic and social dimensions not defined.
7.	Fernandes et al. (2017) [57]		Design strategies method in the design process	Yes	Design solution and recommendation	(i) Directly toward the design stage. (ii) Characteristics not listed according to TBL.
8.	Alli and Sazwan Mohd Rashid (2019) [29]		User Emotional	Yes	user/customer perceive	(i) Directly toward the design stage. (ii) Characteristics not listed according to TBL.
9.	Pacelli et al. (2015) [60]		Industrial scrap	Yes	Design method for design products based on scrap reuse	(i) Directly toward the design stage. (ii) Characteristics not listed according to TBL.
10.	Mokhtar et al. (2016) [58]		Supply chain	Yes	Design phase score metric	(i) Directly toward the design stage. (ii) Three TBL characteristics listed accordingly. Supply chain influences the TBL.
11.	Gotzsch (2008) [65]		Eco-friendly characteristics	Yes	Model of product attraction	(i) Directly toward the design stage. (ii) No characteristics listed according to TBL.
12.	Rossi et al. (2013) [62]	Design Process	Ecodesign guideline	Yes	Integrated eco-design and ecoknowledge in PDP	(i) Directly toward the design stage. (ii) Economic and social dimensions not defined since the research focused on eco-design and did not define all characteristics.
13.	Carulli et al. (2013) [63]		Voice of the Customer (VOC)	Yes	methodology based on Virtual Reality (VR) technologies to support the capturing of the VOC	(i) One of the design processes captured VOC using VR/VP. (ii) Not listed, and characteristics provided according to TBL since the study focused on customer needs.
14.	Flores-Caldero´n et al. (2010) [64]		Redesign product	Yes	Redesign products using Bio-thinking	(i) Directly toward the design stage. (ii) No specific characteristics.
15.	Moreira et al. (2015) [61]		Integration in the design process	Yes	Integration framework	(i) Integration focused on the entire process. (ii) TBL characteristics not listed accordingly, since this work focused on developing a new framework for the product development process.
16.	Großmann et al. (2005) [66]		Methodically supported the product development process	Yes	Comprehensive product development process	(i) Directly toward the design stage. (ii) No characteristics listed according to TBL.
17.	Papahristou and Bilalis (2016) [59]		3D Technologies for design and digital solution	Yes	Integrated PDP with 3D virtual simulation of design concepts on mannequins	(i) Directly toward the design stage. (ii) No characteristics listed according to TBL, since this was adopted through SCAP2020.
18.	Kuo and Wang (2019) [31]	Design Criteria	Integrate different design criteria and guideline	Yes	Functional requirement and design matrix	(i) Directly toward the design stage. (ii) No characteristics listed according to 3 TBLs.
19.	Mesa et al. (2018) [67]		Circular Economy	No	set of sustainability indicators	(i) No direct focus on design process, but development indicated. (ii) Consider adopting the proposed method.
20.	Hassan et al. (2013) [68]		Sustainability performance evaluation	Yes	Evaluation using AHP	(i) Directly toward the design stage. (ii) TBL listed accordingly, obtained from a literature review on the evaluation hierarchy.
21.	Inoue et al. (2012) [69]	Design Preference	Decision-making support	Yes	Set-based design method	(i) Directly toward the design stage. (ii) TBL listed accordingly, obtained from a literature review, to be selected for further consideration.
22.	Ahmed et al. (2019) [84]	Design Decision	Decision support technique	Yes	Set of Experience Knowledge Structure (SOEKS) and Decisional DNA	(i) Directly toward the design stage. (ii) TBL characteristics not listed accordingly, especially for the economic and social dimensions.
23.	Ameli et al. (2019) [70]	Design Optimization by Simulation Model	Integrates design alternative selection and EOL option	Yes	Optimization modeling	(i) Directly toward the design stage. (ii) TBL characteristics listed accordingly. (iii) Complex parameters developed purposely to create a simulation model.
24.	Hapuwatte and Jawahir (2019) [71]		Incorporates predictive models	Yes	Optimization modeling	(i) Directly toward the design stage. (ii) TBL characteristics not listed accordingly, and most of the sustainability concerns were converted into metrics.
25.	De Paula and Rozenfeld (2015) [72]		Analyze the Mass Properties Management problems and solutions	Yes	A process reference model fordesign and mass optimization	(i) Integration focuses on the entire process; TBL not clearly defined. (ii) The variables related to product performance, such as weight, will contribute to sustainability.
26.	Eigner et al. (2014) [73]		System Lifecycle Management	Yes	System modeling	(i) Integration focuses on the entire process. (ii) TBL not listed characteristics accordingly, and limited to the environmental dimension.
27.	Hoffenson et al. (2013) [75]		Tolerance and pricing decisions Influence a product developing	Yes	Tolerance and design optimization approach	(i) Directly toward the design stage. (ii) TBL characteristics not listed accordingly.
28.	Eigner et al. (2011) [74]		Product Lifecycle Management	Yes	Monitoring sustainability performance	(i) Integration focuses on the entire process. (ii) TBL characteristics not listed accordingly.
29.	Leibrecht et al. (2004) [76]		Product lifecycle	Yes	Product and process data information model using a modeling language	(i) Integration focus on the entire process life cycle. (ii) TBL characteristics not listed accordingly and not explicitly defined.
30.	Raoufi et al. (2019) [77]	Design Evaluation and Assessment	Set of analysis methods and software tools	Yes	Method and tools selection	(i) Directly toward the design stage (ii) TBL is an essential metric used for assessment. This could be available in software, especially for the environment dimension.
31.	Turan et al. (2016) [78]		Design evaluation	Yes	Assessment model of fuzzy algorithm	(i) Directly toward the design stage. (ii) TBL characteristics not listed accordingly.
32.	Simões et al. (2013) [79]	Design Evaluation and Assessment	Environmental and economic life cycle analysis of 2 possible materials	Yes	LCA integrated model	(i) Directly toward the design stage. (ii) A social dimension was not defined, since the research focused on environmental and economic analysis.
33.	Panarotto and Törlind (2011) [80]		Customers’ sustainable viewpoints	Yes	A new method for sustainability (Sustainability Innovation Workshop-SIW) (symbol and colors labeling system.)	(i) Directly toward the design stage. (ii) TBL characteristics not listed accordingly.
34.	Donnelly et al. (2004) [81]		Environmental management systems	Yes	Product-based environmental management system	(i) Integration focused on the entire process (ii) Not listing TBL characteristics accordingly, especially for the economic and social dimensions.
35.	Persson (2001) [82]		Eco-indicators	Yes	Types of eco-indicator and design structure matrix	(i) Directly toward the design stage. (ii) TBL characteristics not listed accordingly, especially for the economic and social dimensions.
36.	Veroutis and Fava (1996) [83]		Design for Environment (DfE)criteria	Yes	DfE Criteria Mapping Matrix	(i) Directly toward the design stage. (ii) TBL characteristics not listed accordingly, especially for the economic and social dimensions.
37.	Teixeira and Junior (2019) [85]	Strategic Planning	Sustainability Strategic Planning in business management	Yes	A business guideline involves in PDP	(i) Integration focused on the entire process. (ii) TBL characteristics are defined through the parameter and element, and the variable can be changed according to the case.
38.	de Medeiros et al. (2018) [25]		Alignment between environmental sustainability and the product the development process of SMEs	Yes	A reference model for sustainability in PDP	(i) Integration focused on the entire process. (ii) TBL was not defined accordingly, but is summarized as a sustainable practice through overall PDP.
39.	Teixeira and Junior (2018) [86]		PDP strategic planning	Yes	Strategic Planning of the Integrated Sustainable Products Development Process (PEPDIPS)	(i) Integration focus ranged from design to product launch. (ii) TBL was not defined accordingly. Sustainability is measured through its maturity level.
40.	Pitta and Pitta (2012) [87]		Blue ocean strategy	Yes	Products Development Process (PDP) Matrix	(i) Integration focused on the entire process. (ii) TBL characteristics not listedaccordingly. Strategic planning provided, with six paths and four action plans.
41.	Ny et al. (2008) [88]	Strategic Planning	Significant sustainability challenges and opportunities for a product category in the early development phases.	Yes	“templates” for sustainableproduct development (TSPDs)	(i) Integration focused on the entire process. (ii) TBL characteristics not listed accordingly.
42.	Kara et al. (2005) [89]		Integrating environmental sustainability in manufacturing firms	Yes	An integrated framework to be implemented in the Sustainable Product Development (SPD).	(i) Directly toward the design stage. (ii) TBL characteristics not listed accordingly. Features are identified as strategic planning.
43.	Mesa et al. (2020) [90]	Design Strategies	Modularity tools	Yes	LCA and Sustainability performance	(i) Directly toward the design stage. (ii) TBL characteristics not listed accordingly.
44.	Kaspar and Vielhaber (2017) [91]		Lightweight material	Yes	Material selection in design process	(i) Directly toward design stage. (ii) TBL characteristic not listed accordingly. (iii) Social aspects not well defined; focus was on lightweight technical performance.
45.	Tingström et al. (2006) [93]		Sustainability management	Yes	ABB GATE Model	(i) Integration focused on the entire process. (ii) TBL characteristics not listed accordingly and not fully defined.
46.	Dangelico et al. (2013) [32]		Integration of knowledge andcompetencies for manufacturing and product design process	Yes	External integrative abilities regarding the integration of environmental issues into NPD	(i) Integration focused on the entire process. (ii) 3TBL characteristics not listed accordingly, as a different variable was defined to achieve the outcome.
47.	Fernandes and Canciglieri (2014) [92]		Generating design alternatives directed towards sustainable development	Yes	Conceptual model of Method Integrated Product Development Oriented for Sustainability	(i) Directly toward design stage. (ii) Economic and social dimensions not clearly defined.
48.	Brones and Monteiro De Carvalho (2015) [94]	Integration of Eco-Design	Eco-design integration	Yes	New eco-design integration model	(i) Integration focused on the entire process. (ii) Focused on PDP level through model review.
49.	May et al. (2012) [95]		Sustainable practice Assessment	Yes	Sustainability Integration and Life Cycle Thinking in the NPD process.	(i) Integration focused on the entire process. (ii) TBL characteristics not listed accordingly since this studies the sustainability drivers and barriers in general.
50.	Germani et al. (2013) [96]	Eco-Design Tool	Integrate eco-design activities within the traditional flow of the product design process through the development of an integrated software platform	Yes	Set of software tools (G.EN.ESI)	(i) Directly toward the design stage. (ii) TBL characteristics not listed accordingly and not detailed. They could be vary based on the different criteria, company objectives, and products.

presents a summary of all reviewed articles and establishes 29 environmental, 46 economic, and 62 social characteristics. The traits are evident in all of the case studies and needed to be investigated and improved to create the ideal elements that could be further used in the design stage and become a standard for sustainable furniture design.

Previous articles did not clearly measure the triple bottom line. The studies only proposed and identified different characteristics, variables, parameters, or measurements through their different approaches. To date, no definite characteristics were proposed for wooden furniture design. This is the research gap that will be further highlighted and established in future works to ensure that all furniture industries can employ a new standard with respect to sustainability characteristics.

5. Sustainability Characteristic in a Summary

A deeper understanding of the three dimensions of sustainability is investigated in this study. Through the classification of themes conducted in the previous section, in Section 4, a sustainability characteristic was identified. This covers 137 characteristics in total, of which 29 pertain to the environment, 46 to the economy, and 62 to the social dimension. Figure 1, Figure 2 and Figure 3 depict the predominant sustainability traits in relation to the three most frequently cited dimensions in the literature.

The sustainability characteristics, and the respective product sector, can be used to find the probability characteristic. This can be utilised and ranked among the regularity characteristics used to develop the framework in this study, as shown in Table A3, Table A4 and Table A5. The product sector was also identified through the previous case study review and ranked in accordance with the best case study to determine their respective characters.

The product sector consists of 8 cases for household appliances; 4 cases for each product sector, including electric, electronic equipment, textiles, and healthcare/medical products; 3 of each case involving automotive/components and parts, digital electronic devices, and furniture/components and parts; 2 cases from machine elements and household goods; and one case for fashion/apparel, industrial equipment, human-power vehicle/bicycle, children’s equipment, unmanned aerial vehicle, heavy working machinery, mailing equipment, aerospace/aircraft, and product packaging. Ten of the studies being reviewed were not related to the focus of the case study, which concentrates on sustainability reviews and the development of a sustainability framework for product development and design.

6. Characteristic Selections in Detail

As previously displayed in Table A3, Table A4 and Table A5, the furniture characteristics of Dangeli-co et al. [32], Baeriswyl and Eppinger [55], and Hassan et al. [68] were carefully combined with the other criteria to identify more information on the characteristic selection for further testing and evaluation.

There are 10 environmental characteristics, 17 economic characteristics, and 16 social characteristics that need to be considered when developing the new framework for assessing furniture design in the Malaysian furniture industry, as listed in

Table 1. Furniture sector’s characteristics.

Environment	Economic	Social
Manufacturing/ Process/Assessment/Remanufacture, Recycling, Reuse, Disassembly, Inspecting, Disposal, EOL Material Energy Waste Resource Pollution/Emission Regulation/Certification/Policies Hazardous/Health and Safety Labelling Function	Manufacturing/Remanufacturing/Process/Prod. Cost Material/Material Cost Cost optimization (revenue, product price, EOL, etc.) Energy Cost Energy Efficiency Worker/Labour Cost Storage Cost Packaging/Packaging Cost Transportation/Trans. Cost Maintenance Cost Recovery Cost Repair Cost Consumer Injury Cost Consumer Warranty Cost Modularity Profitability Quality/Reliability New Technology	Hazardous/Health and Safety Manufacturing/Process Ergonomic Human Resources Technical Know-How Price Supply Chain Market Trends/Opportunity Aesthetic Upgradable/Reconfigurable Take-Back Option/Policy Work Ethics User Satisfaction Quality/Reliability Control and Repair (Maintenance) Collaborative and Equity

. To identify suitable characteristics for furniture design, an in-depth analysis was conducted by mapping the characteristics in Table 1, which focus on the main criteria for the furniture sector.

The mapping process was conducted to identify the ideal characteristics of the research issues. This study selected the characteristics using relevant keywords, which are the early design stage, wooden furniture, and sustainability design, to find the research gap according to the sustainability element or triple bottom line, as shown in Figure 4.

Therefore, specific characteristics will have a large impact on the study and will help to improve the sustainable design of wooden furniture in the early design stage. Priority will be given to the early stages of the design process, and a sustainable design will be chosen during the product conceptualization. The design process has the greatest influence on how well an organization or product caters to the awareness of sustainability [70,97]. A sustainability tool must be used to evaluate the sustainability criteria, along with intensified sustainability planning and the design guidelines used when implementing sustainability in conceptual design [98].

Figure 5 shows the ideal sustainability characteristics, whichwere in line with the study’s concerns regarding the wooden furniture industry, furniture design, and sustainability. Sustainability characteristics are finalised thoroughly according to their suitability for implementation, which include five (5) characteristics for environmental dimension, two (2) characteristics for economic dimension, and five (5) characteristics for social dimensions.

Thus, each character was assigned a sub-criterion to ensure that the implementation will enhance the assessment process.

Table A6. Characteristics and Subcriteria.

Sustainability Element	Characteristics	Subcriteria
Environment	Material	Material selection [25,57,62,67,71,75,79,84,85,91,93]
		Minimise and reduce material used [25,32,56,65,77,90]
	Energy	No energy supply during product usage [65]
	Manufacturing	Design suitable for recycling [25,30,31,32,55,60,67,68,70,71,73,75,78,81,82,88,92,96]
		Design suitable for assembly and disassembly [31,55,57,67,70,71,75,82,96]
		Design suitable for reusability [31,60,67,68,70,71,81]
		Design suitable for remanufacturing [32,67,68,70,71]
		Design suitable for disposal [73,81]
		Design suitable for modularize [90,93]
		Design suitable for upgrading [67,82,92]
		Design suitable for maintainance [67,68,92]
		Component simplification [60,67,75]
	Pollution (Waste)	Product specified by reducing a number of parts or components [30,31,57,83]
		Identify material specification to reduce defects and damage [57,71,85]
		Reduce or eliminate hazardous material/waste [23,57,64,67,68,69,75,81,83,88,93]
		Increase product lifetime [29,62,82]
	Policy	Design follows environmental and safety standards/policies (Local and international) [30,78,81,84,96]
		Materials are environmentally certified [32,61]
		Environmental policies used to educate user during use stage [90]
		EcoLabelling in Malaysia—SIRIM Certified Eco-labelling [99,100,101]
Economic	Material cost	Designer identification regarding material availability in Malaysia [15]
		Material changes in product variants [67,68]
		Reuse of material, or material parts or components [60,69]
		Reduce product weight [55,91]
		No additional treatment or coating [55]
		Lower price to increase demand [75]
	Production cost (designer’ sunderstanding of production method, based on material and technology use)	Choice of specific production processes [60,62,91,103]
		Defined according to the bill of materials [30]
		Reduce assembly time [85]
		Recyclability benefit rate [67]
		Implement DFA, DFM, or DFMA approach [28,75]
		Product discard rates [75]
		Lower defects [31]
		Employ as few manufacturing steps as possible [55]
		Minimize packaging [55]
Social	User satisfaction	Usability [29,54,65]
		Accessibility [29,54]
		Customer behaviour [80]
		Sustainable product knowledge shared with the user [85]
		Confidence [31]
		Complaints/Feedback [67,68,75]
		Product variants [67]
		Open architecture products, which user is able to customize [90]
		Design for reliability and durability [67,92]
		Design for attachment and trust [67]
		Precise tolerance [75]
Social	Health and Safety	Ergonomic [29,58,65,67,68]
		Customer requirement [93]
		Health and safety awareness [23,55,58,64,67,68,71,77,93,95]
		Design for reliability (Safety) [92]
	Supply chain	Local manufacture [54]
		Supplier collaboration [32,58]
	Market Trend	New green products [32,61,88]
		Consumer acceptability [61]
		Implementation of product families [67,75]
		Product’s attributes/features [75]
		Adapting to external trends [87]
	Aesthetic	Equally able to support technical performance and quality [29,30,31,55,75,78]
		Sustainability value can be communicated with users [65]

shows the characteristics and subcriteria referred to by previous studies.

6.1. Future Direction

The literature review helped to seek the the triple bottom line possibilities with respect to sustainable characteristics. These sustainability characteristics will be employed to address possible specific design guidelines in more detail. By establishing a design methodology, tools, standards, and regulations, this will help researchers and designers to better understand the characteristics, subcriteria, and design guidelines and yield sustainable furniture design and sustainable product design [15].

6.1.1. Environment—Material

Material is the most important aspect, because it affects the ecodesign approach [30]. It is an established characteristic that acknowledges that sustainable design can lessen the negative effects on the environment and increase energy-efficiency [29]. Therefore, natural and non-toxic materials should be used to satisfy the eco-friendly requirements [31], and this should also be the designer’s primary consideration when selecting a manufacturing method [71]. Therefore, besides the generation of ideas and designs that can penetrate the market, material changes and reduction sare also a main priority in the product development process [90]. As a guide to the designer assessing the materials, the following subcriteria are discussed as tabulated in

Table 2. Material Subcriteria Design Guideline.

Subcriteria	Design Guideline	References
Material Selection	(i) List of restricted materials, which prioritizes the use of recyclable and non-hazardous materials.	[25,67,75,93]
	(ii) Compare materials in terms of their different design structures and consider the material properties (e.g., mechanical and chemical).	[71,79,92]
	(iii) Prefer high-quality materials that significantly influence the separation time for all components.	[62]
	(iv) Identify the product’s lifespan and its product life cycle for appropriate material.	[92]
	(v) Identify the manufacturing process for appropriate material.	[84]
	(vi) Lightweight materials.	[85,91]
Minimise and reduce the material used	(i) Monitor quantities of the material used for products, packaging, and promotional items.	[56,65]
	(ii) Reduce and eliminate unwanted, unnatural, or toxic materials.	[32]
	(iii) Decrease raw material use and change to alternative materials.	[25,90]
	(iv) Reduce part mass	[77]

.

6.1.2. Environment—Energy

Energy is also a prominent character that should be considered when focusing on sustainability. According to the design criteria identified by Kuo and Wang [31], a sustainable product must use less energy. Hapuwatte and Jawahir [71] also described that sustainable production can be attained by taking the energy aspect into account. Consequently, energy-saving through products will improve energy efficiency [85,90]. The following subcriteria are discussed in

Table 3. Energy Subcriteria Design Guideline.

Subcriteria	Design Guideline	References
No energy supply during product usage	(i) Considering a product with low energy consumption or without an energy supply that could save energy.	[65]

, to serve as a guide for the designer when evaluating energy.

6.1.3. Environment—Manufacturing

Effective design and manufacturing processes vigorously promote the quality of product innovation. The innovation trend influences manufacturing feasibility through industrial design, playing an essential role in this process [28]. Thus, the adaptation of manufacturing abilities, such as designs for disassembly, reuse, and remanufacturing, is considered in the design stage [70]. The following subcriteria are discussed in

Table 4. Manufacturing Subcriteria Design Guideline.

Subcriteria	Design Guideline	References
Design suitable for recycling	(i) Identify the ratio of recycling material to the total amount of material used.	[25,32,55,60,67,68,71,75,78,82,88,92]
	(ii) Products are easy to recycle at the end of product life, based on to the material used.	[25,30,31,32,55,67,68,70,71,73,81,92,96]
Design suitable for assembly and disassembly	(i) A new product must be designed efficiently for disassembly.	[31,67,70,71,75,82,96]
	(ii) Identify the joints and fasteners that are easy to access and separate using standard tools.	[55,67,75]
Design suitable for assembly and disassembly	(iii) A new product assembly must be precisely measured for gap and alignment.	[75]
	(iv) A new product assembly must have minimal installation and maintenance steps.	[57]
Design suitable for reusability	(i) Product that can be reused at the end of product life without changing its primary function and quality.	[31,67,68,70,71,81]
	(ii) Product or components/scraps/waste can be used for further development.	[60]
Design suitable for remanufacturing	Products can be remanufactured at the end of their life without changing their major function and quality.	[32,67,68,70,71]
Design suitable for disposal	Product waste is safe to dispose of according to the material used.	[73,81]
Design suitable for modularise	(i) Product must be designed with extended features that can be added, substituted, or removed to make another version or variety of products.	[90,93]
	(ii) Easy to assemble and disassemble by focusing on the joints.	[90]
Design suitable for upgradability	The product must be designed to be useful under changing conditions by improving the quality, value, and effectiveness of the performance	[67,82,92]
Design suitable for maintainability	To increase product lifetime and minimise material and waste.	[67,92]
Component simplification	The product must be designed to maintain its functional abilities and should be possible to restore in good condition after damage to increase the product lifetime.	[60,67,68,75]

as a guide for the designer when evaluating the manufacturing aspect.

6.1.4. Environment—Pollution

Pollution will occur if not considered during the design stage. Mesa et al. [67] explained that one of the main aspects of the environmental impact would be pollution and emissions due to the product development activities, which generate solid (land), liquid (water), and gaseous (air) waste. In addition, the current market trend toward increasing the number of product variants contributes to an increased generation of emissions [90] and more greenhouse gas emissions during product usage [71].

Table 5. Pollution Subcriteria Design Guideline.

Subcriteria	Design Guideline	References
Specification of the product by reducing the number of parts or components	(i) Eliminate unusable or nonfunctioning parts or components, especially for the EOL impact.	[31,57]
	(ii) Specify the component functions	[30,83]
Identify material specification to reduce defect and damage	Identify material weight through material properties and improve the component or part resistance based on material specifications.	[57,71,85]
Reduce or eliminate hazardous material/waste	(i) Identify and list the substitution of hazardous material/ substances for an alternative material.	[57,64,68,81,83,88,93]
	(ii) Identify and list the relationship between components with the material and its end-of-life scenario.	[69]
	(iii) Design comparison based on the concept solution.	[23]
	(iv) Product or components designed with different variations in their use.	[67,75]
Increase Product lifetime	(i) Reduce product replacement by adopting the modular design and being able to upgrade for another function.	[82]
	(ii) Increase technical function.	[29,62]

presents the main subcriteria that can serve as a guide for the designer when evaluating the pollution aspect.

6.1.5. Environment—Policy

To enter the market, furniture design must adhere to the policy standard, which involves implementing strict regulations. Adopting a policy standard is essential to improve product sharing and connectivity between product design support tools [84]. Rossi et al. [30] also posited that compliance with the standards is mandatory for product innovation. For instance, the manager’s product disposal method will benefit the user when the policy-oriented approach is adopted [90]. As a guide to the designer assessing the policy aspect, the following subcriteria are discussed in

Table 6. Policy Subcriteria Design Guideline.

Subcriteria	Design Guideline	References
Design follow environmental and safety standards/ policy (Local and International)	Refer to the environment and safety standard/policy as the primary requirement	[78,84]
	ISO 14040:1997; ISO 14041:1998; ISO14042 [draft]; ISO14043 [draft]; ISO 14062:2002	[81]
	ISO/TR 14062	[96]
	ISO 14006; ISO 14001	[30]
The material used is environmentally certified	Manufactured following international environmentally sustainable standards (fabrics, textile, fibres, yarns, etc.)	[32,61]
Use environmental policy to educate user during the use stage	More attention needs to be paid to the information about reusability or recyclability at the point of final disposal.	[90]
Ecolabelling in Malaysia Context— SIRIM Certified Eco-labelling	The product complies with the Malaysian policy and standard offered by SIRIM QAS to enable the products to be certified as environmentally friendly and enhancing green consumerism.	[99,100,101]

.

6.1.6. Economic—Material Cost

The material cost needs to be understood during the design stage and essential criteria should emphasise economic factors [67]. As Kaspar and Vielhaber [91] suggested, material selection plays a critical role in determining the overall cost of the entire product. Manufacturers should efficiently manage resources, especially materials, to reduce costs, since the production volume has drastically increased [77].

Table 7. Material Cost Subcriteria Design Guideline.

Subcriteria	Design Guideline	References
Material availability in Local area	Designer identifies and utilises the material produced in the local area and compensates for the use of limited resources.	[15]
Material Changes in Product Variant	The designer identifies different materials with product variants by considering the cost of using other materials.	[67,68]
Reuse of material	The amount of material used.	[69]
	Reuse scrap as an additional material when designing a product.	[60]
Reduce product weight	The designer identifies the product weight through design to minimise the amount of material used.	[55,91]
No additional treatment or coating	The designer identifies the materials used that do not require additional treatment or coating.	[55]
A lower price to increase demand	Identify the recyclability of materials to decrease product price and minimise the components that are discarded.	[75]

discusses the following subcriteria as a guide for the designer when evaluating the material cost aspect.

6.1.7. Economic—Production Cost

The designer should consider and prioritize the cost of production when implementing ecodesigns in industrial practice [30]. However, designers lack an in-depth knowledge of this field, which will increase costs when design changes are made [102]. The designer will only be given a standard process to follow during the production of the furniture to ensure that they understand how this characteristic will influence their design. The following subcriteria are discussed in

Table 8. Production Cost Subcriteria Design Guideline.

Subcriteria	Design Guideline	References
Choose specific production process [60,62,91]	Identify the specific standard production process, such as:	[103]
	(i) Rough Milling (ii) Sawing Operations (iii) Band-Saw (iv) Shaper (v) Router (vi) Borer (vii) Mortiser (viii) Tenoner (ix) Lathe (x) Joint formation (xi) Abrasive Sanding Process (xii) CNC Machines (xiii) Through-Feed Machine Lines (xiv) Finishing and Surface Coating (xv) Packaging of Finished Goods
	Define according to the bill of materials	[30]
	Reduce assembly time	[85]
	Recyclability benefit rate	[67]
	Implement DFMA approach	[28]
	Product discard rates	[75]
	Lower defects	[31]
	Employ as few manufacturing steps as possible	[55]
	Minimise packaging	[55]

to help the designer understand the production cost aspect.

6.1.8. Social—User Satisfaction

Product sustainability development requires approaching users to ensure that sustainability awareness is acceptable and applicable. Mesa et al. [90] posited that the global market has focused on sustainability by catering to modular and open-architecture products to ensure user satisfaction. However, evaluating the product family can satisfy the user by generating different product variants [67]. Product sustainability development emphasizes the user expectation of gaining satisfaction, which drives product innovations [80]. The subcriteria discussed in

Table 9. User Satisfaction Subcriteria Design Guideline.

Subcriteria	Design Guideline	References
Usability	The ease of use and comprehension of the entire product should be prioritized when considering its functional aspects.	[29,54,65]
Accessibility	The sustainable product is easy to access and affordable for current and future use.	[29,54]
Customer behaviour	Explore and understand different kinds of customer behaviour regarding sustainability that require design changes toalign with customer behaviour.	[80]
Product knowledge sharing	The product promotes users’ sustainable product care and awareness of related information.	[85]
Confidence	The product inspires users to use sustainable products.	[31]
Complaints/Feedback	The product continuously adapts to the user’s experiences and perceptions to encourage product improvement.	[67,68,75]
Product variant	The component can be shared among product variants using a basic product platform.	[67]
Open architecture products	The product uses a modular design strategy to allow for user customization while in use.	[90]
Design for reliability and durability	The product design has high wear and tear resistance and safety features to avoid failure and malfunction.	[67,92]
Design for attachment and trust	The product is designed to enhance the variety of its functions, which enables users to feel better.	[67]
Precise tolerance	The product is designed with precise tolerance to decrease faulty parts and increase product quality by analysing critical dimensions.	[75]

can serve as a guide for the designer when evaluating the user satisfaction aspect.

6.1.9. Social—Health and Safety

An emphasis on health and safety will indicate the levels satisfaction and social well-being among consumers and workers [23,69]. May et al. [95] identified that most companies implemented health and safety policies as a strategy for sustainability initiatives, but these are not adequately integrated into product development. Thus, some criteria should be considered to enhance health and safety in the social element, such as ergonomic and occupational health [58,67].

Table 10. Health and Safety Subcriteria Design Guideline.

Subcriteria	Design Guideline	References
Ergonomic	(i) The design suits human nature and behaviour. (ii) The design communicates and assists the consumer in using the product. (iii) The design is developed to provide long-lasting comfort and pleasure. (iv) Functionality provided by the product for the consumer.	[29,58,65,67,68]
Customer requirement	The requirement should be identified in the early process and compiled with sustainability planning.	[93]
Health and safety awareness	(i) Identify the level of risk and dangerous factors that should be considered during the product development phase. (ii) Implement and comply with the target based on the ISO 45001- Occupational Health and Safety (Auditing and certification).	[58,64,67,68,93,95]
Health and safety awareness	(iii) Identification of occupational injury rates, illnesses, working and non-working days, and hazardous levels. (iv) Identification of dangerous material in use and labour risk.	[64,71,77]
	(v) Product must introduce a safety rating.	[71]
	(vi) Provide details and labelling on the proper handling of hazardous materials.	[55]
	(vii) Product a concept comparison regarding material safety.	[23]
Design for reliability (Safety)	The product must be designed with a low discard rate, improve structural properites, and lower damage deriving from misuse.	[92]

illustrates the following subcriteria as a guide for the designer when evaluating the health and safety aspect.

6.1.10. Social—Supply Chain

One aspect of sustainability that receives less consideration during the design phase is the supply chain [58]. This is a critical factor, allowing for furniture industries to become competitive in the market and minimize the environmental impact [32]. Thus, the company must manage the supply chain’s effectiveness in leading green product development and controlling irresponsible manufacturing processes [25,59]. The following subcriteria are discussed in

Table 11. Supply Chain Subcriteria Design Guideline.

Subcriteria	Design Guideline	References
Local manufacture	Product parts, components, and materials are locally manufactured and must be easily accessed to minimise their dependence on imported goods.	[54]
Supplier collaboration	Product information should be shared across the supplier chain during the design phase to assist the designer in searching for the idea, comparing and purchasing the sustainable materials, the use of technology and the production process.	[32,58]

to serve as a guide for the designer as they evaluate the supply chain component.

6.1.11. Social—Market Trend

Market trends anticipate current and future product development directions, including the implementation of sustainability, multifunctional use, and product attributes [88]. Companies that comprehend and comply with the sustainable green path will bring new opportunities to the market segment [32,87]. Therefore, to ensure that customers support the sustainable product trends, companies must be conscious of customers’ preferences [61] and explore the sustainability trends in product development [67]. The following subcriteria are discussed in

Table 12. Market Trend Subcriteria Design Guideline.

Subcriteria	Design Guideline	References
New green products	(i) The design must be related to the production process (see Table 10) and the type of material (see Table 8). (ii) The product can be used in many applications. (iii) The product can reduce or avoid electric consumption (see Table 9).	[32,61,88]
Consumer acceptability	Have an in-depth knowledge of customers’ background and preferences.	[61]
Implementation of product families	The products’ design and manufacturing processes can be shared.	[67,75]
Product attribute/ features	The product is considered to have a lower price and higher quality, and is environmentally friendly.	[75]
Adapting to external trends	Identify consumers’ present lifestyles, such as the do-it-yourself (D.I.Y) concept, work from home, or urban garden.	[87]

to serve as a guide for designers as they evaluate the market trend aspect.

6.1.12. Social—Aesthetic

Another aspect that should not be left out is the aesthetical consideration during product development. This is also necessary to ensure product quality [31]. Furthermore, society’s trust in a product is based on how it communicates with its users through its functions and pleasures. Aesthetics can last for a long time and have a positive impact on the environment [65]. The following subcriteria are discussed in

Table 13. Aesthetic Subcriteria Design Guideline.

Subcriteria	Design Guideline	References
Equal to support technical performance and quality	The product is strong and rigid in terms of its shape, form, texture, and uses a suitable colour.	[29,30,31,55,75,78]
Sustainability value to communicate with users	(i) Appeal to the relevant community of consumers or users. (ii) Product looks and feels natural to express its sustainable value.	[65]

to serve as a guide for the designer when evaluating the aesthetic aspect.

7. Summary and Main Findings

This review shows that the right model, related to the triple bottom line, has not been identified to date. The sustainability characteristics were not standardized during the design process in the furniture industry. Therefore, it is necessary to understand the existing sustainability characteristics and the triple bottom line model to ensure a sustainable assessment result when making product decisions.

Our review has also highlighted the importance of choosing the right sustainability characteristics, which align with the triple bottom line model to enhance product performance, such as material use, product structure, human wellbeing, and product costing.

The article aims to show that the triple bottom line framework supports the design of sustainable wooden furniture. This aim has been achieved. A thorough state-of-the-art analysis reveals that the characteristics of designed wooden furniture can be broken down into specific sub-criteria and arranged using the triple bottom line framework with guidelines based on the scientific literature. The classification of the designed furniture as sustainable is justified by its fulfilment of these sub-criteria. Our review has determined that, considering the research gaps in the literature:

• Due to the inconsistencies in the employment of sustainable characteristics, there is a huge need for the establishment of appropriate sustainable characteristics as a standard in wooden furniture designs. In this way, furniture-making, and other, industries can implement these sustainability expectations globally.
• The triple bottom line model must be acknowledged to effectively achieve the sustainable development of a new product and market, which provides further opportunities for the furniture industry. In addition, this will make the design process more effective, ensuring a good sustainability practice, and offers many benefits for businesses, such as reduced product costs, high-quality products, and changing consumer behaviour towards a knowledge of sustainability.