Assessing European Consumers’ Willingness to Pay for Sustainable Laundry Detergents: A Choice Experiment Approach

Abstract

The environmental impact of laundry detergents is a growing concern due to their chemical composition, production processes, disposal methods, and packaging waste. Understanding consumer preferences for sustainable detergents is essential to promoting environmentally responsible choices while ensuring product quality. This study explores European consumers’ willingness to pay for sustainable detergent using a Choice Experiment (CE) framework, integrating attributes such as packaging materials, surfactant composition, washing temperature, efficiency, and price. A survey of 304 respondents across Europe revealed a preference for sustainability-related features, particularly reduced plastic packaging and renewable surfactants, over attributes like washing temperature and efficiency. Generational, socioeconomic, and regional differences influenced willingness to pay (WTP), with Spanish consumers, Baby Boomers, and higher-income groups showing the highest WTP. Despite positive attitudes towards sustainability, the study highlighted an attitude–behavior gap, where stated preferences did not always align with purchasing behavior, suggesting that performance and cost remain key factors. The findings highlight the need to align technological advancements with consumer expectations, balancing sustainability, performance, and affordability to drive the adoption of eco-friendly detergents. These insights provide valuable guidance for researchers and industry in advancing efforts that enhance market acceptance of environmentally sustainable laundry products across Europe.

1. Introduction

The environmental impact of consumer products is significant and multifaceted, influencing ecosystems, climate, and human health throughout their lifecycle. From raw material extraction to disposal, these products contribute to deforestation, pollution, greenhouse gas emissions, and persistent waste, particularly single-use plastics. Among these impacts, single-use plastics have attracted significant attention for their lasting presence in the environment. However, the environmental footprint of consumer products extends beyond packaging waste. Many products have an intrinsic impact through their composition, production, and usage that often involves complex chemical formulations and energy-intensive processes, which exacerbate environmental pressures [1].

Laundry detergents have a considerable environmental impact due to their chemical composition, manufacturing processes, and disposal methods. This contributes to critical issues such water quality, ecosystem health, and human well-being [2,3]. Life Cycle Assessments (LCAs) reveal that the in-use phase of laundry detergents—especially energy-intensive washing processes and user habits and practices—accounts for approximately 60% of their carbon footprint. The environmental burden of laundry detergents is also influenced by their ingredients, accounting for approximately 20% [4]. Conventional detergents often contain phosphates, surfactants, and non-biodegradable components that exacerbate eutrophication, harm biodiversity, and pose long-term risks to aquatic ecosystems and human health through contamination of water and food chains. Furthermore, single-use plastic packaging exacerbates solid waste challenges [5,6].

Transitioning to eco-friendly laundry practices offers an opportunity to mitigate these impacts. Strategies such as using biodegradable detergents, washing at lower temperatures, and adopting sustainable packaging have the potential to significantly reduce the environmental footprint of household laundry. For example, washing clothes at lower temperatures is a concrete example of how the effect of technological development—i.e., using enzymes that are effective at lower temperatures in formulations—and conscious consumer habits—i.e., adopting even small decreases in washing temperature—can synergistically yield substantial energy savings and, consequently, a reduction in greenhouse gas emissions [7,8]. Conscious consumer habits, such as optimizing washing programs and reducing wash frequency, can amplify these benefits, potentially cutting energy and water consumption by up to 50% [9,10,11].

Consumers also play a crucial role by making informed purchasing choices. Supporting companies that prioritize eco-friendly practices encourages sustainable production. Choosing products made from recycled materials, favoring durable goods, and recycling at the end of a product’s lifecycle further minimizes waste and environmental impact. Combining sustainable laundry habits with responsible purchasing and disposal practices allows individuals to significantly contribute to a greener future [12].

European consumers, increasingly aware of their role in promoting sustainability, are prioritizing environmentally friendly purchasing decisions, reflecting greater environmental awareness and social responsibility. Studies [13,14,15,16] show a growing willingness to pay a premium for eco-friendly products, with over a third of global consumers favoring eco-conscious options [17]. In the detergent market, 72% of European consumers actively consider sustainability when making purchasing decisions, reflecting a growing preference for features such as biodegradable ingredients, a reduction in chemical toxicity, and sustainable packaging [18,19,20]. These factors collectively reflect the growing importance of minimizing ecological and human health impacts within the detergent industry.

Despite this progress, the transition to sustainable detergents poses challenges. Consumers demand high performance, cost-effectiveness, and convenience from detergents [4,21], and achieving widespread adoption requires balancing these needs with environmental goals, as well as aligning technological advancements with consumer expectations. For example, while washing at 20 °C could reduce energy use, the lack of effective enzymes at such low temperatures’ limits feasibility. Addressing these socio-technical challenges is crucial to ensuring both environmental sustainability and consumer satisfaction in the detergent market.

2. Literature Review

In the industrial landscape, the market success of a product often depends on how effectively it meets consumer needs and expectations, while being introduced in a timely and effective manner [22]. Understanding consumer preferences and purchasing behavior is crucial for shaping successful product launch strategies and marketing plans, which are key to driving business performance.

The detergent industry, serving a broad and diverse consumer base, has been extensively studied to identify the attributes most valued by consumers. Kamwendo and Maharaj, in a study conducted in South Africa, identified product form as the most critical determinant of consumer preference. Their findings revealed a strong preference for liquid detergents over powder and bar formats, reflecting a shift towards convenience and performance. Interestingly, price emerged as a less significant factor in the decision-making process, suggesting that consumers are willing to pay more for products that offer superior functional attributes, such as cleaning efficiency and stain removal capabilities. Consumers expressed a preference for smaller packaging (1 kg) suitable for about two weeks of use. Demographic factors, including gender, age, and socio-economic status, were found to significantly influence these preferences, underscoring the need for tailored marketing strategies [23]. Chandru et al. emphasized the importance of brand reputation and product quality as primary drivers of consumer choice in the detergent market in India. Promotional offers, prices, and advertising were secondary factors, underscoring the need for manufacturers to focus on quality and strategic branding to maintain competitiveness. Their analysis revealed significant links between demographic factors and purchasing motivations, providing practical insights for market segmentation and strategy formulation [24]. Similarly, Nwamara reported that cleaning performance (58.3%) is the most important attribute driving consumer choice in Nigeria, followed by price (45.8%). Other factors, such as product popularity, packaging, scent, and recommendations, played smaller roles in decision-making [25].

Sustainability has become a critical factor in consumer preferences within the laundry detergent market [18,19,20]. Whitson et al. note a significant shift since 1996 towards preferences for eco-labels and phosphate-free formulations, driven by willingness to pay higher prices for sustainable options [26]. For instance, a study in Malaysia reported that 79.5% of consumers were willing to pay a premium for eco-friendly laundry detergents [27]. Similarly, Das and Tyagi, through a study conducted across various countries, identified a growing demand for products that combine high performance, such as effective stain removal and low-temperature cleaning efficiency, with sustainability features—including biodegradability, reduced energy and water use, and eco-friendly ingredients [28].

Despite the growing interest in sustainability, cleaning performance remains the top priority for laundry detergent users. Key attributes, such as effective stain removal, brightness, and odor elimination, significantly influence customer satisfaction and trust in the product. Studies reveal that when eco-labeled detergents fail to meet these expectations, consumers often engage in compensatory behaviors, by using more detergent or washing at higher temperatures. Therefore, the challenge for manufacturers is to develop detergents that offer both high performance and eco-friendly characteristics. Products that deliver on both fronts are more likely to meet consumer expectations, encourage sustainable habits like cold-water washing and reduced dosing, and foster satisfaction and environmental benefits [4,21].

This challenge is complicated by the well-documented “attitude–intention–behavior gap”: while many consumers expressed positive attitudes toward eco-friendly products, these intentions frequently fail to translate into consistent sustainable actions. Numerous studies highlight this discrepancy [29,30,31,32,33], showing that while many consumers value sustainability in theory, actual purchasing and usage behaviors often prioritize performance over environmental concerns. This underscores the need for products that not only address environmental concerns but also meet the consumers’ functional expectations.

The Choice Experiment (CE) is a stated preference methodology used to identify the factors that influence purchasing decisions of both producers and consumers. This approach, which finds widespread application in marketing and behavioral research, facilitates the elicitation of individual preferences for complex goods and services by evaluating multiple attributes simultaneously, rather than focusing on a single characteristic [34]. This technique allows researchers to identify the attributes that most significantly influence purchasing behaviors and to estimate the value of goods and services based on their characteristics and perceived demand [35,36].

The CE method has been recognized as an effective tool for analyzing consumer preferences for consumer goods, including those with sustainability attributes [37]. It has been widely applied to investigate preferences across a variety of consumer goods categories—such as food, packaging, textiles, cosmetics, and domestic appliances [37]. Although several studies have addressed sustainability aspects in laundry detergents, few have employed a Choice Experiment approach to systematically evaluate consumer preferences for multiple eco-friendly product attributes. This highlights a methodological gap that this study aims to address.

The few existing studies applying Choice Experiment to laundry detergents have predominantly focused on attributes unrelated to sustainability. Kamwendo and Maharaj examined consumer preferences for general product attributes in detergents without consideration of their environmental impact [23]. Buchmüller et al. investigated consumer decision-making regarding frequently used chemical household products, including laundry detergents, but without emphasizing sustainability [38]. Findrik and Morawetz explored valuation changes due to health information without integrating sustainability-focused attributes [39]. Towhidul Islam and Louviere used CE to assess the stability of aggregate-level preferences for laundry detergents, but their analysis did not include sustainability dimensions [40].

Few studies have specifically incorporated sustainability attributes into CE studies of laundry detergents, and those that do often focus on isolated aspects. Jo, M. et al. examined consumer preferences for biodegradability and the natural versus chemical composition of detergents [41]. Kholod, M et al. focused mainly on intangible brand attributes such as advertising and in-store promotions. Product attribute data consist only of attributes such as the amount of surface-active agent (%) and bleach (binary), as well as the type of package, standard amount of the detergent for 30 L of washing, and net weight [42]. These studies, however, provide limited insights into the broader sustainability characteristics of detergents, as their attribute sets typically include only basic and isolated features. The limitation of studies integrating a comprehensive set of sustainability attributes into the CE framework for laundry detergents highlights a critical gap in the literature and the need for further research to gain a more complete understanding of consumer decision-making in this domain.

3. Aim of the Study

The aim of this study is to investigate the key drivers of sustainable detergent consumption by examining consumer preferences and the factors influencing purchasing decisions within a Choice Experiment (CE) framework.

The definition of sustainability that guides this analysis is the integration of environmental responsibility into product development and consumer behavior, aiming to reduce the negative impact of products across their life cycle, in line with the principles of sustainable consumption and production promoted by the United Nations Sustainable Development Goals.

This research adopts a holistic approach, integrating multiple sustainability attributes such as packaging materials, surfactant composition, and energy-efficient washing temperatures, offering a multidimensional perspective on sustainable detergent consumption. Additionally, the study analyses the consumers’ trade-offs between sustainability, cost, and product performance, providing novel insights into the decision-making processes behind detergent purchases. Unlike previous studies that have often considered sustainability attributes in isolation or focused primarily on brand-related factors, this study explores both product-specific features and behavioral drivers, including socioeconomic, demographic and psychological factors such as environmental awareness and habitual practices. By promoting the adoption of eco-friendly laundry practices and products, this research aims to reduce the environmental impact of household activities and guide technological innovation and corporate research, offering actionable insights for academia and industry and ensuring new developments align with consumer priorities and sustainability goals.

4. Materials and Methods

4.1. A CE Workflow to Minimize Methodological Biases

The current study builds on the framework presented by Saija et al. [37], which developed a systematic CE workflow for the analysis of consumer products, with particular attention paid to sustainability attributes, aimed at reducing methodological biases and ensuring reliable results across various sectors. This workflow served as the methodological foundation to both structure the survey on which the CE approach is based and analyze the collected responses, ensuring consistency and robustness in the findings.

4.2. Target Product

In the experimental design, the identification of the target product and its key features that consumers prioritize when purchasing laundry detergents were informed by a comprehensive literature review, with some of the main findings being summarized in the Introduction Section. A detailed analysis of articles, reviews, textbook chapters, and publications from 2015 to 2025, particularly from the last four years (2021–2025), was conducted through databases such as Google Scholar, PubMed and Elsevier, using targeted keywords to explore aspects like detergents, sustainability, purchase choice and consumers.

Findings from Kamwendo and Maharaj [23], highlighting a pronounced consumer preference for liquid detergents over other formats, with a clear inclination towards smaller packaging sizes, guided the selection of the target product to be used in the study. Based on these insights, the current study focuses on a standard laundry liquid detergent in a 1.5 L format. This choice was motivated by the familiarity of the product among consumers of all age groups and genders, thereby minimizing potential bias in the respondent data.

4.3. Attributes and Levels

The identification of attributes and levels was based on a multistage process involving an extensive literature review (as reported in Section 2) and consultations of sectoral experts. This iterative approach ensured that the selected attributes reflected the priorities of laundry detergent consumers.

Attributes in the context of Choice Experiments represent the key characteristics or features of the good or service under evaluation. Each attribute is designed to capture a specific dimension of consumer preference or product quality [35]. For this study, the most significant factor, apart from the detergent format, was product quality. Specifically, product performance emerged as a non-negotiable criterion, with a particular emphasis on cleaning efficiency and effective stain removal at low washing temperatures. These characteristics align with consumer interest in achieving energy savings. In addition to performance attributes, considerations of sustainability were integral to the selection process. Packaging design and the amount of surfactants were identified as key factors influencing both environmental sustainability and consumer purchasing decisions. Price was also included as an essential attribute for implementing the CE methodology effectively.

Levels define the range of variation within each attribute, representing the different possible states or intensities of the attribute that respondents might consider during the decision-making process [35]. In this study, the determination of levels for each attribute sought to represent the full range of options available in the market, always including a “standard” option. The price ranges were chosen considering values that could be representative of detergent prices in all European countries. The reference workflow outlined by Saija et al. [37] guided this process, recommending the use of 3–5 attributes and 10–15 levels to capture the most relevant product features without overloading respondents and minimizing cognitive bias. The final list of selected attributes and their corresponding levels is presented in

Table 1. Final list of selected attributes and levels for laundry detergent (1.5 L).

Attribute	Level	Acronym	No. of Levels
Efficacy in stain removal	Standard removal	SR	2
	Stubborn stain removal	SSR
Recommended washing temperature	Standard temperature (40–60 °C)	ST	3
	Save energy (30 °C)	30T
	Maximum energy saving (20 °C)	20T
Packaging	Standard packaging	SP	2
	Recycled and recyclable plastic	RRP
	−70% of plastic *	−70P
Surfactants	Standard use	SS	3
	Renewable and sustainable surfactants	RSS
	−20% surfactants *	−20S
Price	3 €	3 €	4
	4.5 €	4.5 €
	6 €	6 €
	7.5 €	7.5 €

* Compared to the standard scenario.

.

4.4. Experimental Design

The Choice Experiment adopted in this study is based on the Coordinate Exchange Algorithm (CEA), which generates efficient designs for the questionnaire. The CEA optimizes the design of the questionnaires by iteratively refining an initial layout, considering changes on an attribute-by-attribute basis to achieve improved configurations. By adopting this iterative approach, the algorithm minimizes the D(B)-error r based on a multinomial logit model. This process ensures the generation of well-structured, informative datasets, facilitating robust data collection for subsequent analysis. The algorithm was implemented through the Idefix package in the R software environment (version 2023.12.1+402), slightly adapting the model proposed by Traets et al. [43] and Pérez-Troncoso [44]. By systematically exploring possible attributes and level combinations, the algorithm generated a design comprising 12 choice sets, each presenting three alternatives. In the context of discrete Choice Experiments, a choice set is defined as a scenario presented to respondents, containing multiple mutually exclusive alternatives from which they are asked to select their preferred option. Each alternative represents a product or service described through attributes and levels [35]. In this study, although the reference workflow design suggests that using 8–9 choice sets is optimal for minimizing biases, the algorithm required a minimum of 12 choice sets to achieve a feasible and efficient experimental configuration based on the number of attributes and levels included in the study. While this choice slightly exceeds the recommended range, it ensures that the design captures the necessary complexity of consumer preferences without compromising the validity of the results.

The three options included in the choice sets are two product profiles (“Option A” and “Option B”) and a “No-choice option”. According to the workflow design, the inclusion of the no-buy option allows respondents flexibility to reject all presented alternatives, thereby simulating realistic decision-making scenarios and improving the external validity of the findings.

A pilot study, created by assuming that all the priors of the efficient design are equal to zero, was conducted to assess the feasibility and effectiveness of the methodology and test the validity and reliability of the questionnaire, data collection procedures, and result analysis before scaling up to a larger sample. The preliminary results obtained from the pilot study were also used as new priors to refine the algorithm in an iterative approach that resulted in the final design of the study.

4.5. Questionnaire Design

The questionnaire, provided in the Supplementary Materials, was distributed to consumers using Google Forms and disseminated through various communication channels, including emails, social media platforms, direct messaging, and sponsored campaigns. To ensure a wider distribution of the survey to different respondents’ categories, the questionnaire was distributed in 4 languages: English, Spanish, German, and Italian.

Participation was voluntary and anonymous. Respondents gave their consent after being informed about the purpose of the research, how their answers would be used, and their right to withdraw at any time, ensuring transparency and ethical compliance. Questionnaires were anonymous and no personal data were collected.

The questionnaire was structured into four main sections to facilitate a comprehensive analysis of respondents’ preferences, characteristics, ideas, and habits. These sections included the following: (1) detergent purchasing choices, (2) socioeconomic and demographic information, (3) detergent shopping and usage habits, and (4) interest in sustainability.

The detergent purchasing choices (1) featured the 12 choice sets generated during the experimental design process. Respondents were instructed to imagine themselves in a supermarket scenario and tasked with selecting a detergent. Each choice set presented two detergent options with distinct attributes, alongside a “none of the above” (no-buy) option to simulate real-world decision-making scenarios. The two purchase options were highlighted using labels to replicate typical shopping conditions and draw attention to key product attributes. Such labels are pivotal for enhancing consumer understanding of sustainability benefits, which aligns with marketing strategies to promote green or bio-based consumer goods. A description of one of the choice cards used in the survey is shown in Figure 1.

The socioeconomic and demographic information (2) comprised seven questions designed to collect key respondent characteristics, including gender, age, employment status, educational attainment, type of residence, income, and country of residence. These variables were essential for a detailed analysis of the responses, as previous studies have demonstrated their significant influence on consumer preferences and behavior [37].

The questions outlining detergent shopping and usage habits (3) focused on the frequency of detergent purchases and the household member primarily responsible for this task. These data provided valuable insights into the context of respondents’ choices, enabling a more accurate interpretation of the responses.

Finally, the interest in sustainability section (4) included four targeted questions to investigate respondents’ awareness and attitudes toward sustainability-related issues, thereby enhancing the overall relevance of the study by double checking the consistency of the responses.

The main differences between the pilot questionnaire and the final questionnaire included a streamlining of the explanatory content provided at the beginning of the survey to retain respondent attention, the expansion of language options from two (Italian and English) to four (Italian, English, French, and German) to reach a broader consumer audience, and the revision of specific questions to improve clarity and effectiveness. Additionally, as recommended by Saija et al. [37], an explanation banner was introduced for each attribute and level to minimize interpretation bias (Figure 2). These refinements significantly reduced potential biases and maximized the quality and reliability of the results.

4.6. Sample Selection

A sample of 44 consumers, predominantly Italian, was considered for the pilot study. At this preliminary stage, the sample was not designed to be homogeneous in terms of country of residence or socioeconomic and demographic characteristics, as these variables were not critical to the objectives of the pilot phase aimed at testing the methodology and refining the experimental design.

For the final study, a sample of 304 European consumers was targeted. No specific selection criteria were applied, adhering to the principle that any individual could represent a potential consumer of laundry detergent. The aim was to collect as many responses as possible while ensuring a distribution that was broadly representative of key socioeconomic and demographic variables.

4.7. Result Analysis: The Conditional Logit Model

The methodology for the analysis and interpretation of results is based on the Random Utility Maximization (RUM) framework, a widely utilized theoretical model for CE that assumes individuals act to maximize their utility.

The adoption of this framework facilitates the evaluation of preferences by estimating the utility or relative importance individuals assign to various attributes and levels within the context of Choice Experiments (CEs) [35]. According to RUM modeling, an individual n (compared with a total of N individuals) faces J alternatives across T multiple choice occasions. The utility (U_njt) derived by individual n from an alternative j during a choice occasion t is calculated as

U_njt = V_njt + ϵ_njt,

where V_njt represents the deterministic (or representative) utility, and ϵ_njt is the random component accounting for unobserved factors. The error term ϵ_njt follows a joint density distribution of the random vector denoted f(ϵ_n) = f (ϵ_n1, ϵ_n2,…, ϵ_nJT). The deterministic utility V_njt is typically modeled as linear in parameters:

V_njt = x′_njtβ

where x_njt is a vector of attributes associated with alternative j and β, which represents the coefficients to be estimated.

For the present study, the utility function was modeled as follows:

U_ji = β1 × stainij + β2 × temperatureij + β3 × packagingij + β4 × surfactantij + β5 × priceij + ϵij + β0 × nobuy,

where i = 1, 2,…, n represents the respondents, j denotes the choice alternatives (e.g., option 1, option 2, or the “no-buy” option), and no-buy is a binary variable indicating whether the respondent chose none of the available options. The variables stainij, temperatureij, packagingij, surfactantij and priceij correspond to the attributes being evaluated (Table 1), while priceij is the monetary attribute expressed as a continuous variable. The term ϵij represents the random error component, capturing unobserved influences on the respondents’ choices.

The analysis of the results involves the use of R software to operationalize the Conditional Logit Model (CLM) by implementing and adapting the work performed by Pérez-Troncoso [44] and Barriviera [45].

To further analyze preferences, the willingness to pay (WTP) for each attribute was calculated using the following formula:

WTP = −(coefVar/coefPrice).

where coefVar represents the estimated coefficient of the attribute under consideration, and coefPrice is the estimated coefficient of the price attribute. This calculation provides a monetary value reflecting how much respondents are willing to pay for changes in specific attributes, offering a tangible measure of the attributes’ perceived importance.

5. Results

5.1. Pilot Study Results

The pilot study involved interviewing a small group of participants without specific attention paid to their sociodemographic and geographical characteristics, as these were deemed to be non-critical for the pilot phase objectives. A sample of 44 consumers was selected for the study. The majority of participants were Italian (95%) and female (61%). The sample predominantly consisted of younger individuals, with 84% of respondents being under the age of 34, and was highly educated, as 86% of participants held at least a bachelor’s degree. Furthermore, most respondents (89%) were directly responsible for purchasing household detergents.

The pilot study provided a set of priors (

Table 2. Priors derived from the pilot study.

alt3.cte	SR	ST	30T	4.5 €	6 €	7.5 €	RRP	SP	ST	−20S
−1.98	0.31	−0.70	0.49	0.97	0.43	−0.30	0.37	−0.58	−0.40	−0.16

) used to refine the experimental design and design the final study. For a more immediate interpretation of the coefficients, they were reported with only two significant figures instead of the seven typically provided by R. This simplification does not have a practical impact on the interpretation of the results, ensuring clarity without compromising accuracy.

Although these priors were derived from a small, non-representative sample and were not intended to provide conclusive results, they offer initial insights into consumer utility perceptions. Positive utility values suggest that participants were already inclined to pay more for certain attributes, while negative values indicate a lack of willingness to pay. Specifically, attributes such as stubborn stain removal (SR), lower washing temperature (30T), and recycled and recyclable packaging (RRP) showed positive utility, pointing to a preliminary preference for both functional effectiveness and sustainability features. These early indications helped validate the structure of the Choice Experiment and supported the selection of relevant attribute levels for the final study design.

5.2. Final Study Results

The questionnaire developed in this work was administered to a total of 304 European consumers, having different nationalities and socioeconomic and demographic characteristics. The results of the respondents’ profiles and preferences are described in the following sections.

5.2.1. Sample’s Profile Results

The respondents’ profiles were assessed using the socioeconomic and demographic information section included in the questionnaire (detailed in the Supplementary Materials), with the results presented in

Table 3. Results of the socioeconomic and demographic information section of the questionnaire.

Variable	Range	Frequency	Percentage
Age	18–24	43	14.1%
	25–34	106	34.9%
	35–44	58	19.1%
	45–54	35	11.5%
	55–64	45	14.8%
	65+	17	5.6%
Gender	Female	197	64.8%
	Male	107	35.2%
Employment	Employee	200	65.79%
	Self-employed 1	18	5.92%
	Unemployed 2	8	18.75%
	Retired	21	2.63%
	Student	57	18.75%
Education	No title	3	1%
	High School Diploma 3	58	19.1%
	Higher Education Diploma	4	1.3%
	Bachelor’s degree	61	20.1%
	Master’s Degree	94	30.9%
	Second-Level Postgraduate Master’s	2	0.7%
	Ph.D.	81	26.6%
	Postgraduate Specialization Course	1	0.3%
Annual household income	EUR < 20,000.00	47	15.5%
	EUR 20,000–EUR 40,000	105	34.5%
	EUR 40,000–EUR 60,000	64	21.1%
	EUR 60,000–EUR 80,000	40	13.1%
	EUR > 80,000	48	15.8%
Residence Type	Private home (rented or owned)	107	35.20%
	Apartment (rented or owned)	135	44.4%
	Apartment shared with students	20	6.6%
	University residence	6	1.97%
	Living with parents	36	11.8%
Country	Italy	129	42.4%
	Spain	79	26%
	Germany	35	11.5%
	Portugal	23	7.6%
	UK	9	3%
	Sweden	7	2.3%
	Switzerland	5	1.6%
	Austria	3	1%
	Others 4	8	2.6%
	Non-European countries 5	4	1.3%

¹ Both entrepreneurs and households are included in this category; ² Included within this category are housewives; ³ Both technical and educational degrees are included in this category; ⁴ This category includes Belgium, France, and the Netherlands with 2 responses each, and Denmark and Finland with 1 response each; ⁵ This category includes Russia and the USA with 2 responses each, and New Zealand and Zambia with 1 response each.

, which provides a summary of key descriptive statistics characterizing the sample population.

To simplify the analysis, some categories included in Table 3 were grouped together. Specifically, age groups were categorized as Generation Z (18–24), Millennials (25–34), Generation X (35–54), and Boomers (55+). Employment statuses were combined into employed (self-employed and employee) and unemployed (students, unemployed and retired). For education, diplomas (no title, high school diploma and higher education diploma) were grouped together, as were master’s degrees (master’s degree and second-level postgraduate master’s); the highest educational levels (Ph.D. and postgraduate specialization courses) were also merged.

As shown in Table 3, the sample is primarily composed of Millennials (25–34 years, 34.9%) and Generation X (35–54 years, 30.6%), with minimal representation from Boomers (55+, 20.4%) and Generation Z (under 25, 14.1%). Women make up the majority of the sample (64.8%), which could influence gender-specific analyses.

Most participants are employed (71.7%) or students (18.75%), reflecting an active and professional population. The educational level is notably high: 30.9% hold a master’s degree, while 26.6% have achieved the highest education levels (Ph.D. or postgraduate specialization).

Income distribution centers around EUR 20,000–EUR 40,000 (34.5%), with significant representation in higher brackets. This spread indicates a middle-to-upper class socioeconomic profile. Most respondents reside in private homes or apartments (79.6%), with a smaller portion in shared or university housing (8.6%), highlighting predominantly independent living arrangements. This categorization facilitates a clearer and more concise interpretation of the findings.

The geographic distribution reveals a concentration of respondents in Italy (42.4%), followed by Spain (26%) and Germany (11.5%). Other European countries, such as Portugal (7.6%) and the UK (3%), are less represented. Non-European countries account for only 1.3%, emphasizing a primarily European sample.

The sample is skewed toward a young, female, and highly educated demographic with a middle-to-upper socioeconomic status, primarily residing in Europe. This profile should be considered when interpreting the findings.

5.2.2. Consumer Habits and Preferences in Sustainability

The analysis of consumer habits revealed notable trends in laundry practices. Nearly 55% of respondents reported performing 2–3 laundry cycles per week, while a significant portion (24%) indicated engaging in 0–1 cycle per week. Together, these two categories encompass approximately 80% of the surveyed population, reflecting generally sustainable practices among respondents, even if the frequency of laundry in the first group suggests range for improvement in reducing water and energy consumption.

Additionally, nearly 85% of the sample reported active involvement in purchasing decisions, underscoring the relevance of their responses. This finding indicates that the respondents possess a notable awareness of the detergent market and their preferences regarding product characteristics, reinforcing the validity of the insights derived from the survey.

Regarding sustainability perceptions, the responses to two key questions revealed strong support for sustainable consumer practices. Approximately 82% of respondents believe that shifting toward sustainable consumer products is “somewhat” or “very” important in combating climate change. Similarly, 88% of respondents highlighted the significance of adopting sustainable purchasing behaviors.

5.2.3. Respondents’ Preferences for Detergent Purchasing

The results of the respondents’ preferences, based on CLM, have been evaluated first on the entire sample and then by making distinctions between different sociodemographic categories in order to assess specific drivers in different categories. For the first analysis, the results are shown in

Table 4. Attribute utility coefficients obtained with R software using the Conditional Logit Model.

Attribute	Level	Acronym	Coefficient *
Efficacy in stain removal	Stubborn stain remover	SR	+0.85
	Standard removal	SSR	−0.85
Recommended washing temperature	Standard temperature (40–60 °C)	ST	−1.87
	Save energy (30 °C)	30T	+1.02
	Maximum energy saving (20 °C)	20T	+0.85
Packaging	Standard plastic	SP	−2.51
	Recycled and recyclable plastic	RRP	+1.17
	−70% of plastic	−70P	+1.34
Surfactants	Standard use	SS	−2.51
	Renewable and sustainable surfactants	RSS	+1.23
	−20% surfactants	−20S	+0.78
Price			−0.55
alt3.cte			−4.24

Note: * p < 0.05.

. To facilitate a clearer and more immediate interpretation, the coefficients have been reported with only two significant figures instead of the five typically provided by R. This reduction in precision does not affect the practical interpretation of the results, ensuring readability without compromising the validity of the analysis.

The CLM results reveal significant drivers of consumer choice. The negative coefficient for the alternative-specific constant (−4.24, p < 2 × 10⁻¹⁶) suggests that the “none of the above” option was generally less preferred, highlighting a strong consumer tendency toward active product selection. All coefficients for the attributes that were hypothesized to be improvements over the standard are positive, indicating that there is indeed an increase in utility for these features. This confirms consumer preference for enhanced attributes. Considering the Δ, as shown in Figure 3, or the difference between the high and low coefficients of each attribute, packaging attributes emerge as the most relevant to consumer preferences. The Δ for “Recycled and recyclable plastic” (3.68) and “−70% of plastic” (3.85) significantly surpasses that for “Stain removal efficacy” (1.70) and “Washing temperature” (2.89, 2.72), emphasizing the priority given to sustainable materials. Notably, the Δ for “Washing temperature” (over 2.7) highlights strong interest in energy efficiency, with preferences for “Save energy (30 °C)” and “Maximum energy saving (20 °C)” exceeding those for stain removal efficacy. While the Δ for “Surfactants” is smaller, it still indicates a preference for fully renewable options. Despite price sensitivity (coefficient: −0.55344), the large Δ values for sustainability and efficiency suggest that consumers are willing to pay more for environmentally friendly and energy-efficient products. These insights provide clear directions for sustainable product design and marketing strategies.

The attribute utility coefficients were used also to calculate the willingness to pay of the subject towards the attributes (

Table 5. Willingness to pay (WTP) for each attribute.

SSR	30T	20T	RRP	−70P	RSS	−20S
+1.54 €	+1.85 €	+1.54 €	+2.11 €	+2.42 €	+2.23 €	+1.42 €

). To ensure that price variations are expressed on a practically applicable monetary scale, the coefficients have been reported with only two significant figures instead of the six typically provided by R. This level of precision is sufficient for meaningful interpretation, as monetary values in real-world pricing are typically rounded to the nearest cent.

The results clearly reflect the trend that consumers are willing to pay a premium for more sustainable products, regardless of the type of attribute. For the efficiency attribute, the WTP for stubborn stain efficiency is EUR +1.54, suggesting that consumers positively value this level. The highest WTP values are observed for sustainable attributes, specifically −70% of plastic in the packaging category (EUR +2.42) and renewable and sustainable surfactants in the formulation (EUR +2.22). Within the Packaging category, the reduction in plastic (−70%) is preferred over the use of recycled and recyclable plastic. For surfactants, renewable and sustainable surfactants exhibit a WTP almost double that for reduction in surfactants, within a gap of approximately EUR 0.8.

Temperature-related attributes show lower WTP values, with consumers willing to pay more for an efficiency level at 30 °C than at 20 °C, with a gap of EUR ~0.3. Overall, these findings provide nuanced insights into consumer preferences, with sustainability and product effectiveness emerging as critical drivers of willingness to pay.

An intriguing inconsistency emerges when comparing these WTP results with the responses to the survey question on the most and least important attributes. While nearly 50% of respondents identified effectiveness as the most important attribute (followed by price at 28%), over 41% indicated packaging as the least relevant attribute (followed by surfactants at 27%). These responses contrast with the WTP findings, where sustainability-related attributes such as packaging and surfactants receive the highest premiums, even surpassing effectiveness.

The analysis of attribute utility coefficients and WTP reveals notable differences across socioeconomic and demographic groups. Italy, Spain, Germany, and Portugal were identified as the most statistically relevant countries due to the higher number of responses, which ensures greater reliability of the results.

The CLM results show that the specific coefficient analyses conducted across various sociodemographic characteristics (annual household income, age, gender, and employment) and geographic areas (countries of origin) align closely with the overall trends (Appendix A,

Table A1. Attribute utility coefficients obtained with R software using the Conditional Logit Model for each attribute according to socioeconomic and demographic information.

Sample	alt3.cte	SR	SSR	ST	30T	20T	SP	RRP	−70P	SS	RSS	−20S	Price
Italy	−4.58	0.91	−0.91	−1.85	1.05	0.80	−2.56	1.13	1.43	−3.22	1.32	1.90	−0.62
Spain	−3.54	0.92	−0.92	−2.08	1.06	1.02	−2.63	1.20	1.43	−3.09	1.25	1.84	−0.41
Germany	−3.31	0.59	−0.59	−1.61	0.95	0.66	−2.17	1.10	1.07	−1.36	0.84	0.52	−0.47
Portugal	−5.34	0.77	−0.77	−2.24	1.08	1.16	−2.78	1.19	1.59	−3.29	1.49	1.80	−0.76
Generation Z	−5.38	0.99	−0.99	−1.88	1.04	0.84	−2.73	1.38	1.35	−2.11	1.44	0.67	−0.66
Millennials	−5.10	0.86	−0.86	−3.01	1.18	1.83	−2.39	1.17	1.22	−1.98	1.25	0.73	−0.69
Generation X	−3.94	0.91	−0.91	−2.10	1.13	0.97	−3.14	1.33	1.81	−2.30	1.32	0.98	−0.55
Boomers	−2.45	0.75	−0.75	−1.58	0.78	0.80	−1.73	0.83	0.90	−1.92	1.11	0.81	−0.30
Employed	−4.18	0.84	−0.84	−1.99	1.08	0.91	−2.59	1.17	1.42	−2.17	1.32	0.85	−0.57
Unemployed	−4.38	0.88	−0.88	−1.61	0.89	0.72	−2.31	1.15	1.16	−1.67	1.03	0.64	−0.52
Diploma	−3.88	0.78	−0.78	−1.11	0.67	0.44	−2.27	1.06	1.21	−1.90	1.22	0.68	−0.46
Bachelor	−3.67	0.72	−0.72	−1.87	0.95	0.92	−2.43	1.16	1.27	−1.91	1.19	0.72	−0.50
Master	−5.46	1.05	−1.05	−1.86	1.06	0.80	−2.60	1.30	1.30	−2.00	1.26	0.74	−0.74
PhD	−5.03	0.92	−0.92	−1.07	1.00	0.07	2.39	−1.00	−0.39	−1.00	0.68	0.32	−0.40
Male	−5.55	1.03	−1.03	−2.35	1.23	1.12	−2.63	1.22	1.41	−2.19	1.28	0.91	0.66
Female	−3.76	0.78	−0.78	−1.66	0.93	0.73	−2.45	1.15	1.30	−2.93	1.20	1.73	−0.51
EUR < 20,000	−4.71	0.58	−0.58	−1.57	0.76	0.81	−2.09	1.07	1.02	−1.75	1.03	0.72	−0.59
EUR 20,000–EUR 40,000	−4.58	0.84	−0.84	−1.71	1.06	0.65	−3.35	1.10	1.25	−1.92	1.17	0.75	−0.60
EUR 40,000–EUR 60,000	−4.33	0.93	−0.93	−1.57	0.82	0.75	−2.62	1.24	1.38	−2.06	1.30	0.76	−0.51
EUR 60,000–EUR 80,000	−3.64	1.02	−1.02	−2.82	1.46	1.36	−3.46	1.37	2.09	−3.08	1.92	1.16	−0.48
EUR > 80,000	−3.65	0.96	−0.96	−2.50	1.25	1.25	−2.73	1.29	1.44	−2.00	1.23	0.77	−0.56

). This finding reinforces the robustness of the model and the reliability of the observed consumer preferences and confirms that sustainability and energy efficiency are consistent priorities for consumers across diverse profiles.

The WTP analysis across socioeconomic and demographic groups highlights important variations in consumer preferences (

Table 6. Willingness to pay of each attribute according to socioeconomic and demographic information.

Sample	SSR	30T	20T	RRP	−70P	RSS	−20S
Italy	+1.46 €	+1.70 €	+1.29 €	+1.82 €	+2.31 €	+2.13 €	+1.45 €
Spain	+2.23 €	+2.57 €	+2.49 €	+2.91 €	+3.49 €	+3.04 €	+2.05 €
Germany	+1.24 €	+2.00 €	+1.39 €	+2.31 €	+2.25 €	+1.77 €	+1.10 €
Portugal	+1.01 €	+1.42 €	+1.52 €	+1.56 €	+2.09 €	+1.96 €	+1.05 €
Generation Z	+1.50 €	+1.57 €	+1.27 €	+2.08 €	+2.03 €	+2.18 €	+1.02 €
Millennials	+1.24 €	+1.70 €	+1.20 €	+1.69 €	+1.76 €	+1.81 €	+1.06 €
Generation X	+1.66 €	+2.06 €	+1.76 €	+2.42 €	+3.31 €	+2.40 €	+1.79 €
Boomers	+2.49 €	+2.59 €	+2.67 €	+2.74 €	+2.99 €	+3.67 €	+2.69 €
Employed	+1.48 €	+1.91 €	+1.61 €	+2.07 €	+2.51 €	+2.33 €	+1.50 €
Unemployed	+1.68 €	+1.69 €	+1.37 €	+2.19 €	+2.21 €	+1.96 €	+1.21 €
Diploma	+1.70 €	+1.47 €	+0.96 €	+2.32 €	+2.65 €	+2.68 €	+1.48 €
Bachelor	+1.46 €	+1.91 €	+1.86 €	+2.35 €	+2.57 €	+2.39 €	+1.44 €
Master	+1.41 €	+1.43 €	+1.08 €	+1.74 €	+1.73 €	+1.69 €	+0.99 €
PhD	+2.28 €	+2.47 €	+0.18 €	−2.5 €	−0.97 €	+1.68 €	+0.80 €
Male	+1.56 €	+1.87 €	+1.69 €	+1.84 €	+2.13 €	+1.94 €	+1.38 €
Female	+1.52 €	+1.83 €	+1.44 €	+2.26 €	+2.55 €	+2.36 €	+1.43 €
EUR < 20,000	+0.98 €	+1.30 €	+1.37 €	+1.82 €	+1.74 €	+1.74 €	+1.21 €
EUR 20,000–EUR 40,000	+1.39 €	+1.76 €	+1.08 €	+1.81 €	+2.07 €	+1.94 €	+1.23 €
EUR 40,000–EUR 60,000	+1.84 €	+1.61 €	+1.48 €	+2.45 €	+2.73 €	+2.57 €	+1.50 €
EUR 60,000–EUR 80,000	+2.10 €	+3.03 €	+2.82 €	+2.84 €	+4.33 €	+3.97 €	+2.40 €
EUR > 80,000	+1.70 €	+2.21 €	+2.21 €	+2.30 €	+2.55 €	+2.17 €	+1.37 €

). Among the four countries analyzed, Spanish consumers exhibited the highest WTP values across all attributes, with particular emphasis on packaging (−70% plastic, EUR 3.49) and renewable and sustainable surfactants (EUR +3.04€). Italian and German consumers demonstrated more moderate WTP values, with Italian respondents favoring packaging (−70% plastic; EUR +2.31) and surfactant-related attributes (renewable and sustainable surfactants; EUR +2.13), in line with the Spanish preferences. German consumers were more focused on packaging attributes. Portugal displayed the lowest WTP values overall, especially for formulation and temperature-related attributes.

Generational differences also emerged from the analysis. Baby Boomers consistently showed the highest WTP values across most attributes, reflecting a stronger preference for both product effectiveness and sustainability. Younger generations, including Generation Z and Millennials, demonstrated lower overall WTP but placed greater emphasis on sustainability attributes, such as renewable surfactants and reduced or recycled plastic packaging.

Gender differences in WTP were also observed. Women tended to exhibit slightly higher WTP for most sustainability-related attributes, particularly for packaging (−70% plastic, EUR +2.55 compared to EUR +2.13 for men) and renewable and sustainable surfactants (EUR +2.36 compared to EUR +1.94 for men). Conversely, men demonstrated marginally higher WTP for temperature-related attributes, such as washing at 30 °C (EUR +1.87 for men vs. EUR +1.83 for women) and 20 °C (EUR +1.69 for men vs. EUR +1.44 for women).

Employment status had a minimal impact on WTP, with employed respondents showing slightly higher WTP for five out of seven attributes. The largest differences were observed for renewable surfactants (EUR +2.33 for employed vs. EUR +1.96 for unemployed respondents) and energy-saving washing at 30 °C (EUR +1.91 for employed vs. EUR +1.69 for unemployed respondents).

Educational background influenced WTP values as well. Respondents with a diploma and bachelor’s degree exhibited the highest WTP for sustainability-related attributes, particularly for packaging (Recycled and recyclable plastic, EUR +2.32 and EUR +2.35, respectively; −70% plastic, EUR +2.65 and EUR +2.57, respectively) and renewable and sustainable surfactants (EUR +2.68 and EUR +2.39, respectively), while those with a master’s degree showed lower WTP across all attributes. However, individuals with a master’s degree showed a more moderate WTP across all attributes. Notably, PhD holders exhibited the most varied and polarized WTP, with some negative values for plastic-related features (Recycled and recyclable plastic, EUR −2.50; −70% plastic, EUR −0.97), but positive values for performance and energy-saving attributes, such as washing at 30 °C (EUR +2.47) and stubborn stain remover (EUR +2.28).

Finally, the income analysis revealed a positive correlation between income levels and WTP for most attributes, particularly sustainability-related features. Individuals earning below EUR 20,000 exhibited the lowest WTP values. Respondents earning above EUR 60,000 displayed the highest WTP, with packaging (−70% plastic, EUR +4.33) and renewable and sustainable surfactants (EUR +3.97) receiving the greatest premiums. However, for respondents earning above EUR 80,000, WTP values were lower than those in the EUR 60,000 €–80,000 range across all attributes, with −70% plastic (EUR +2.55) and renewable and sustainable surfactants (EUR +2.17) showing a noticeable decrease.

We can therefore conclude that the most generally preferred attributes are those related to sustainability, such as reduced plastic packaging and renewable surfactants, followed closely by energy efficiency and product effectiveness, with variations in preferences influenced by demographic and socioeconomic factors.

6. Discussion

The findings of this study provide valuable insights into European consumer preferences for sustainable detergents, revealing a strong inclination towards attributes associated with environmental sustainability and energy efficiency. The analysis highlights important trends across demographic and socioeconomic groups, highlighting the key drivers of consumer behavior and willingness to pay (WTP) for sustainable product features.

Both the pilot and final studies consistently demonstrate a high level of consumer awareness regarding sustainability. These results underscore that consumers actively recognize their critical role in promoting sustainability through their purchasing choices and behaviors. The alignment observed between consumer awareness, habits, and preferences for sustainable practices is promising and suggests opportunities to further enhance their contributions to environmental goals. These findings align with broader societal trends that emphasize growing consumer awareness of sustainable products and environmentally conscious behaviors. Notably, the majority of respondents expressed a strong belief in the role of sustainable products in mitigating climate change, reinforcing the importance of integrating such features into product development and marketing strategies.

Across the sample, sustainability-related attributes—particularly packaging with reduced plastic and the use of renewable surfactants—emerged as the most influential determinants of consumer choice. This highlights the significant role of sustainable materials in shaping purchasing decisions, with many consumers willing to pay a premium for environmentally friendly products.

Surprisingly, attributes related to washing temperature were not among the highest-valued features, suggesting that consumers prioritize other characteristics over the energy savings associated with lower washing temperatures. Within this category, consumers exhibited a higher WTP for efficiency at 30 °C compared to 20 °C, with a notable gap of approximately EUR 0.30. This trend may reflect a lack of consumer confidence in cold washing, even when equivalent effectiveness is assured. This indicates that while consumers acknowledge the indirect impact of lower washing temperatures on sustainability and cost, they may find it harder to relate to these benefits compared to more tangible attributes, such as reducing plastic waste or using renewable ingredients.

Within the packaging category, a clear preference emerged for reducing plastic consumption by 70% compared to using recycled and recyclable plastics. This suggests that consumers perceive overall plastic reduction as a more impactful solution for environmental sustainability. For surfactants, the difference in consumer preference was particularly relevant: the WTP for renewable and sustainable surfactants was nearly double that for the reduction in surfactant quantities, with a substantial gap of approximately EUR 0.80. This finding may reflect a stronger emotional or perceived environmental benefit associated with renewable surfactants compared to only reducing their quantity. Additionally, consumers might associate reduced surfactants with a potential compromise in product effectiveness, making renewable surfactants more appealing as they align with both sustainability goals and expectations for product performance.

WTP for product efficiency indicates that consumers positively value this attribute. This finding aligns with prior studies emphasizing that consumers are unwilling to compromise on product effectiveness and consider it a critical factor in their decision-making. However, product effectiveness is not the attribute having the highest WTP premium, with consumers demonstrating a stronger interest and willingness to invest in sustainability-related features. A relevant inconsistency arises when comparing the WTP results with responses to survey questions about the most and least important attributes. While nearly 50% of respondents identified effectiveness as the most important attribute (followed by price at 28%), over 41% identified packaging as the least relevant attribute (followed by surfactants at 27%). These responses are in contrast with the WTP findings, where sustainability-related attributes such as packaging and surfactants received the highest premiums, surpassing even product effectiveness. This discrepancy may be attributed to a divergence between stated preferences (survey responses) and revealed preferences (WTP results). One plausible explanation is that survey respondents may rationally prioritize effectiveness and price when explicitly questioned, as these are traditionally viewed as critical factors in decision-making. However, the WTP results suggest that when faced with hypothetical purchasing scenarios, consumers are more emotionally or subconsciously influenced by sustainability-related factors, which may be more in line with their ethical values or broader environmental concerns. This phenomenon could also be attributed to the presence of an attitude–intention–behavior gap [30,46,47], which refers to the discrepancy between the stated values of an individual or organization and their actual actions. While consumers may genuinely express a preference for attributes such as effectiveness and price in explicit surveys, their willingness to pay premiums for sustainability-related features in purchasing scenarios highlights a divergence between their articulated priorities and the choices they make when ethical or emotional considerations come into play. For example, an overlooked but relevant factor in detergent preference is fragrance, which was not included among the evaluated attributes in this study. Fragrance can play a key role in product acceptance, as it contributes to the sensory experience and emotional appeal of the detergent. This is especially relevant for female consumers—who make up the majority of our sample—and who often demonstrate greater sensitivity to product scent in household decisions. While not directly related to sustainability, a detergent’s fragrance can strongly influence perceived quality and satisfaction and may act as a barrier to the adoption of more sustainable alternatives if it fails to meet consumer expectations. This could help explain part of the attitude–behavior gap observed in our results, where sustainability is valued, yet traditional preferences prevail in practice.

Additionally, the lower WTP for effectiveness compared to sustainability might also come from a “baseline assumption” bias [48], where consumers implicitly expect a certain level of effectiveness in all products and are therefore less inclined to pay a premium for it. On the other hand, sustainability attributes may represent added value or differentiation in their perception, justifying a higher WTP.

The analysis of socioeconomic and demographic aspects revealed generational differences in WTP for sustainable product attributes. The results highlight a generational gap, with older consumers willing to invest in both effectiveness and environmental features, while younger consumers prioritize specific sustainability aspects, such as renewable surfactants and reduced plastic packaging, without placing as much emphasis on practical considerations like product effectiveness. Baby Boomers exhibited the highest WTP across most attributes, reflecting a stronger preference for integrating effectiveness and sustainability. This finding was unexpected, as previous research has suggested that younger generations tend to be more environmentally conscious [49,50,51]. However, the higher WTP among Baby Boomers may be explained by their greater financial stability and purchasing power. The income analysis clearly demonstrates a positive correlation between income levels and WTP, with individuals earning above EUR 60,000 displaying the highest WTP values for sustainability-related attributes. This suggests that older consumers, who tend to have higher incomes, are also those most capable of paying a premium for eco-friendly products. In contrast, Millennials and Generation Z, despite showing strong preferences for sustainability, appear to be financially constrained, which translates into a lower WTP in practice. Although younger generations might be more sustainability-conscious in their attitudes, their limited financial resources hinder their ability to translate these preferences into actual purchasing decisions.

While the income analysis supports the trend of higher WTP among wealthier individuals, the data for those earning above EUR 80,000 show a deviation from this pattern. This discrepancy is likely due to the smaller sample size in this income category, making the results less representative. The overall trend remains clear: those most willing to pay for sustainability are also those with higher financial means, reinforcing the idea that affordability plays a crucial role in translating environmental awareness into purchasing behavior.

The results indicate that educational background influences WTP for sustainability-related attributes, yet in an unexpected way. Individuals with higher education levels (master’s and PhD) generally exhibited lower or more polarized WTP values, whereas those with a diploma or a bachelor’s degree showed a greater willingness to pay for sustainable features. This challenges the common assumption that higher education correlates with greater environmental awareness and, consequently, a higher WTP for eco-friendly products. One possible explanation is that higher-educated individuals tend to be more critical and analytical when assessing sustainability claims. This could be linked to greater awareness of greenwashing concerns, where companies exaggerate their sustainability efforts for marketing purposes. On the other hand, individuals with lower or moderate levels of education may be more influenced by sustainability messaging and marketing, perceiving sustainable attributes as a unique value proposition that justifies a higher price. It is also important to note that the polarized and sometimes negative WTP values observed among PhD holders may be partially influenced by the relatively small number of respondents in this category. A smaller sample size can lead to higher variability and less reliable results, meaning that the lower or negative WTP values observed for certain attributes in this group should be interpreted with caution.

Gender differences also emerged as a significant factor in WTP for sustainability-related attributes. Women demonstrated a higher WTP for aspects like packaging sustainability and renewable surfactants. This trend may be due to traditional and contemporary gender roles, where women are often seen as primary decision-makers for household products and are more socially attuned to community and environmental impacts. Furthermore, studies in consumer behavior consistently show that women tend to exhibit stronger pro-environmental attitudes and behaviors compared to men [52,53,54]. Men, on the other hand, displayed slightly higher WTP for attributes related to energy efficiency, such as lower washing temperatures. This preference may stem from an interest in technical efficiency and cost-saving aspects, in line with traditional male traits more focused on pragmatism and utility. These distinct preferences between genders and generations provide valuable insights into tailoring marketing strategies to align with specific demographic segments.

Overall, these findings highlight the importance of considering both generational and gender-specific factors when designing and marketing sustainable products. Tailoring sustainability messaging and product attributes to the preferences of different demographic groups may enhance consumer engagement and adoption of sustainable practices.

The analysis revealed significant variations in WTP across different countries, suggesting that cultural, economic, and policy-driven factors play a crucial role in shaping consumer behavior toward sustainable products. While sustainability is a growing concern across Europe, the degree to which consumers are willing to pay a premium for eco-friendly features varies depending on national priorities, environmental policies, and economic conditions. Spanish consumers exhibited the highest WTP across nearly all attributes, particularly for packaging reduction and renewable surfactants. This could be attributed to a strong cultural emphasis on environmental responsibility, reinforced by public policies and awareness campaigns promoting sustainability. Conversely, Portuguese respondents exhibited the lowest WTP across most attributes, suggesting that sustainability might not yet be a primary purchasing criterion in this market. This could be explained by a combination of economic factors and consumer priorities. Portugal has a lower average income level compared to the other analyzed countries, meaning that price sensitivity remains a significant barrier to adopting sustainable products at a premium price.

7. Conclusions

7.1. Summary of Key Fundings

Sustainability is increasingly influencing consumer purchasing decisions, particularly in the household products sector. As environmental concerns and regulatory demands grow, manufacturers are focusing on developing eco-friendly detergents that meet consumer expectations for sustainability, efficiency, and performance. To successfully integrate sustainability into the market, it is essential to understand which product attributes consumers prioritize and how their willingness to pay (WTP) varies across different demographic and socioeconomic groups. This knowledge can help guide targeted product innovations and ensure that sustainable products are both environmentally beneficial and economically viable.

This study highlights that plastic reduction in packaging and renewable surfactants are the most valued sustainability-related attributes, with consumers demonstrating a willingness to pay a premium for these features. This trend highlights a growing consumer preference for eco-friendly solutions, in line with broader societal shifts toward sustainable consumption and environmental responsibility.

The variations in WTP across sociodemographic groups emphasize the need for adaptable approaches in product development and communication strategies. Younger consumers, who are more engaged in environmental and social issues, may respond better to sustainability messaging that emphasizes ethical responsibility and climate impact. Older consumers, who value both sustainability and functional reliability, may be more likely to adopt sustainable products when innovations enhance cleaning performance while incorporating eco-friendly materials. Additionally, gender differences suggest that women, who generally exhibit a stronger preference for sustainability attributes, may be more receptive to messages highlighting household well-being and environmental responsibility, while men may be more influenced by technological advancements, cost savings, and performance benefits. Given that the primary consumers responsible for purchasing detergents are generally older and predominantly female, marketing efforts should align communication strategies accordingly, emphasizing both the practical and environmental benefits of sustainable detergents. Highlighting efficacy alongside sustainability could further encourage adoption among consumers who seek high-performance cleaning solutions that also align with environmental values.

Geographical differences in WTP further indicate that regional market needs should be considered in sustainability research and product development. In countries with higher WTP for sustainability, such as Spain, investment in premium sustainable formulations and advanced eco-friendly technologies could drive further adoption. In contrast, in markets with lower WTP, such as Portugal, efforts should focus on cost-effective sustainable alternatives to ensure broader accessibility. Additionally, the strong correlation between income and WTP suggests that sustainability efforts should prioritize scalability and affordability, ensuring that sustainable products are accessible to a wider range of consumers, rather than remaining niche premium options.

These findings highlight the importance of scientific, evidence-based approaches in the development of sustainable detergents. By aligning research, innovation, and market strategies with consumer expectations and economic realities, companies can accelerate the transition toward more sustainable household products.

7.2. Industry Implications

The findings of this study provide actionable insights for companies operating in the detergent and home care industry. Consumers demonstrated a clear willingness to pay more for sustainable features, particularly reduced plastic packaging and renewable surfactants, without compromising on product performance. Based on this evidence, several strategic directions can be recommended for industry stakeholders:

• Invest in eco-design by prioritizing packaging solutions that reduce material use (e.g., concentrated formats, refill systems, plastic-free or alternative materials), which consumers perceive as high-value.
• Develop and communicate environmentally friendly formulations, particularly those with bio-based and biodegradable surfactants, aligning with consumer expectations and supporting brand positioning and differentiation.
• Integrate sustainability without compromising performance. Companies should ensure that environmental gains do not come at the expense of cleaning power and that this is properly communicated to consumers. Ensuring that these innovations maintain high product performance while reducing environmental impact will be key to increasing consumer acceptance and long-term adoption.
• Develop more targeted communication and product lines that align with the values and priorities of specific consumer segments to emphasize both ecological and functional attributes. By anchoring R&D and product strategies in empirical consumer data, the industry can accelerate the transition toward scalable and competitive sustainable products.

7.3. Limitations and Future Research

This study has certain limitations that suggest directions for future research. Its geographic scope is restricted to European consumers, with most respondents from Spain, Italy, Germany, and Portugal, while other regions were underrepresented. Future studies should aim for a more balanced sample across Europe to enhance the generalizability of the findings. Additionally, high-income individuals (above EUR 80,000) and those with a PhD were underrepresented, potentially limiting the reliability of results for these groups. Broader inclusion of socioeconomic backgrounds is recommended to strengthen consumer insights. Furthermore, while the Choice Experiment methodology effectively assesses stated preferences, future studies should integrate longitudinal approaches to better account for the gap between consumer intention and actual purchasing behavior.

Moreover, the exclusion of sensory attributes, particularly fragrance, represents a limitation of this study. While not directly tied to sustainability, fragrance can strongly influence product appeal and acceptance. Future research should consider including sensory dimensions to better capture the emotional factors that affect the adoption of sustainable detergents. Finally, although the selected price range was designed to be as representative as possible for all European countries, it is not fully representative of the actual price levels in each individual country. Despite these limitations, this study offers a solid foundation for further research, contributing to both academic understanding and industry strategies for sustainable product adoption.