Badminton Racket Coatings and Athletic Performance: Review Based on Functional Coatings

Abstract

As a key piece of equipment in badminton, the surface treatment technology of rackets has garnered significant attention in the fields of material science and sports engineering. This study is the first to systematically review research on racket coatings, integrating interdisciplinary knowledge on the classification of functional coatings, their performance-enhancing principles, and their relationship with competitive levels, thereby addressing a gap in theoretical research in this field. This study focuses on four major functional coating systems: superhydrophobic coatings (to improve environmental adaptability and reduce air resistance), anti-scratch coatings (to prolong the life of the equipment), vibration-damping coatings (to optimise vibration damping performance), and strength-enhancing coatings (to safeguard structural stability). In badminton, differences in player skill levels and usage scenarios lead to variations in racket materials, which, in turn, result in different preparation processes and performance effects. The use of vibration-damping materials alleviates the impact force on the wrist, effectively preventing sports injuries caused by prolonged training; leveraging the aerodynamic properties of superhydrophobic technology enhances racket swing speed, thereby improving hitting power and accuracy. From the perspective of performance optimization, coating technology improves athletic performance in three ways: nanocomposite coatings enhance the fatigue resistance of the racket frame; customized damping layers reduce muscle activation delays; and surface energy regulation technology improves grip stability. Challenges remain in the industrial application of environmentally friendly water-based coatings and the evaluation system for coating lifespan under multi-field coupling conditions. Future research should integrate intelligent algorithms to construct a tripartite optimization system of “racket-coating-user” and utilize digital sports platforms to analyze its mechanism of influence on professional athletes’ tactical choices, providing a theoretical paradigm and technical roadmap for the targeted development of next-generation smart badminton rackets.

1. Introduction

The badminton racket, as the core force application and control device connecting the athlete to the shuttlecock, directly impacts competitive performance (as shown in Figure 1). With advancements in material science and manufacturing processes, racket materials have evolved from wood and metal to high-performance carbon fiber composites, continuously pushing the limits of lightweight design, high strength, and aerodynamics [1]. However, the surface coating—a critical functional component of the racket—has not received research attention commensurate with its technical value regarding its mechanism of action, performance enhancement pathways, and systemic impact on sports performance [2]. The string bed coating plays multiple irreplaceable roles during play: it precisely regulates the friction coefficient to influence control accuracy and spin effects; it acts as an anti-wear barrier to extend string lifespan and maintain tension stability; it provides environmental protection to delay material aging; and it adjusts tactile feedback to affect shot response [3]. Although the mechanical properties of string core materials have been extensively studied, fundamental research on coating materials—such as polyurethane, fluoropolymers, silicone-based, and nanocomposites—remains insufficient in terms of tribological performance, mechanical property modulus, viscoelasticity, bonding strength, and durability under high-speed impacts, cyclic friction, and complex environmental interactions [4]. Existing tests are mostly limited to single-factor laboratory conditions, making it difficult to accurately reflect the comprehensive mechanisms by which coatings influence shuttlecock speed, spin, placement accuracy, and vibration damping in real-world high-impact, multi-angle, and variable-environment scenarios, leading to discrepancies between experimental data and actual performance [5]. Therefore, systematically reviewing the current state of functional coatings for badminton rackets, clarifying their classification, performance enhancement principles, and relationship with sports performance, is crucial for moving beyond the current reliance on experience and commercial marketing in string selection and guiding the design and scientific selection of high-performance, long-lasting, and environmentally friendly racket strings. This study is the first review of functional coatings for badminton rackets, focusing on the functional mechanisms and performance contributions of the four major coating systems, namelym superhydrophobicity, anti-scratch, shock-absorption, and reinforcement, and analysing their systematic enhancement of racket durability, hitting effect, and athletic performance, as well as pointing out the existing challenges and future directions, with the aim of providing a theoretical paradigm and a technological roadmap for the research and development of next-generation smart badminton rackets.

2. Classification and Characteristics of Functional Coatings for Badminton Rackets

2.1. Superhydrophobic Coating

In competitive sports, the durability of badminton equipment is crucial for player performance. High-humidity venues, player sweat, and moisture from court cleaning may cause the racket strings and frame to degrade due to liquid penetration. As a core technology for enhancing racket durability and functionality, hydrophobic protective films play a vital role by constructing special interfacial barriers [6]. As shown in

Table 1. Durability Challenges of Badminton Rackets and Technical Countermeasures of Coatings.

Failure Types	Cause of Formation	Technical Countermeasures
Mechanical Wear and Peeling	String Friction/Ball Impact	Organic-Inorganic Hybrid Reinforcement Coating Toughness
Chemical degradation	UV/sweat pH	UV absorber + acid-alkali resistant monomer
Loss of interfacial adhesion	Thermal and humidity cycling stress	Plasma substrate activation pretreatment

, their primary functions include material maintenance and performance protection, effectively preventing liquid infiltration, forming a tight hydrophobic film layer on the carbon fiber frame and string surfaces to block various liquid moisture, including sweat, environmental humidity, and cleaning water [7]. Through the application of waterproof coating, the moisture absorption rate of polyester, nylon and other polymer beat threads is reduced, effectively avoiding plasticization caused by humidity, thereby maintaining string bed tension stability and the efficiency of energy transfer during shots [8]. Additionally, the coating isolates moisture, preventing electrochemical corrosion of metal components like grommets and connectors, thereby delaying the decline in structural strength. By optimizing the surface treatment process of the string bed, stable friction performance is achieved [9]. Dry treatment ensures the consistency of the coating’s friction coefficient, effectively preventing humidity fluctuations from interfering with ball control. Furthermore, the application of waterproof technology significantly reduces string water absorption and weight gain, enabling precise control of the racket head’s swing weight parameter, thus ensuring the continuity and stability of swing motions [10]. The waterproof performance characteristics of the coating are achieved by using low-surface-energy materials such as fluorocarbon polymers and silicone resins to prepare superhydrophobic coatings. The directional arrangement of molecular chains weakens water molecule adsorption, resulting in rapid droplet sliding (as shown in Figure 2). By introducing nano-scale silicon dioxide and zinc oxide particles [11,12], a multi-level rough surface is constructed, enhancing the stability of the Cassie-Baxter state, thereby achieving excellent hydrophobic properties.

2.1.1. Enhanced Water and Ice Resistance for Sports Equipment

Checking the literature in the last 10 years, no studies on the performance of superhydrophobic coatings on badminton rackets specifically for badminton rackets were found, but superhydrophobic coatings are sure to improve the waterproof and anti-icing performance of sports equipment and badminton rackets. The application of superhydrophobic coatings can improve the waterproof performance of sports equipment. In a related study, researchers conducted sailing experiments on model boats coated with superhydrophobic coatings to evaluate their drag reduction performance (Figure 3). The experimental results showed that the superhydrophobic coating significantly increased the average sailing speed of the model boat, demonstrating its effective drag reduction capability (Figure 3b). The drag reduction mechanism of the superhydrophobic coating can be summarised in two main aspects: firstly, the coating surface transforms the solid–liquid contact into a solid-gas contact, which effectively reduces friction (Figure 3c); and secondly, the presence of bubbles promotes interfacial slip, which further reduces the friction between the fluid and the ship surface (Figure 3d). The experimental data showed that the average speed of the coated vessel was higher than that of the uncoated vessel, which confirmed that the superhydrophobic coating had a significant drag reduction effect [14].

In addition, the researchers conducted continuous sailing experiments (Figure 3e), which showed that the drag reduction effect remained almost stable with the increase in sailing distance (16.8 m), and the drag reduction rate did not change significantly, which further verified the long-lasting effect of the superhydrophobic coating. In order to evaluate the mechanical robustness of the coating, the drag reduction performance of the coated vessel after wear and tear was tested (Figure 3f). The results showed that the drag reduction rate changed very little, from 28.7% (0.521 m/s) to 26.9% (0.514 m/s), indicating that the superhydrophobic coating has excellent mechanical durability and provides sustained drag reduction performance under prolonged use. Therefore, the superhydrophobic coatings exhibit a good combination of both drag reduction and mechanical stability, making them suitable for long-term underwater applications. As a result, superhydrophobic coatings can be applied to sports equipment such as kayaks to improve performance by reducing water resistance.

Superhydrophobic coatings also show excellent performance in terms of ice resistance. When applied to ski equipment, these coatings are effective in reducing the adhesion of snow and ice, thereby reducing friction and improving speed performance [14]. The superhydrophobic surface of ski equipment prevents snow and ice from adhering and maintains the smoothness and flexibility of the skis even in wet and cold environments, ensuring optimal gliding conditions. This not only increases the skiing speed, but also reduces the physical exertion and difficulty of the athletes during skiing [15].

In extreme environments, the anti-icing ability of superhydrophobic coatings has a significant impact on the performance of sports equipment. For example, in sailing, applying such coatings to sails can effectively prevent icing [16]. Icing increases the weight of the sail and reduces its agility and overall performance. Superhydrophobic coatings ensure that the surface of the sail remains free of ice, keeping it lightweight and efficient. By reducing the ice load, the sails perform optimally even in cold conditions, ensuring the smooth running of the race and the safety of the athletes [17].

2.1.2. Superhydrophobic Mechanism and Coating Construction Technology

Superhydrophobic properties rely mainly on the combined effect of low surface energy materials with micro- and nanoscale rough structures (Cassie-Baxter state) [18]. In these coatings, surface treatments with fluorine-containing substances, such as fluorosilanes or fluoropolymers, or silicone-containing compounds, such as silanes and siloxanes, are commonly used [18]. These materials themselves exhibit strong hydrophobic properties, with contact angles typically ranging from 100 to 120 degrees. The core of achieving superhydrophobic properties lies in the construction of multilevel micro- and nano-rough surfaces. By compounding nanoscale structures on micron-sized bumps, a stable air film layer can be formed between the solid–liquid interface, thus significantly reducing the true contact area between the two [19]. The droplets are mainly supported by the air cushion, which not only enhances the contact angle but also significantly reduces the rolling angle [20]. In racket applications, nanoparticle composite technology is often employed by dispersing hydrophobic nanosilicon dioxide (SiO₂), zinc oxide (ZnO), and carbon nanomaterials in polymer matrices such as polyurethane, acrylic, and epoxy resins, and the coatings are cured to form rough surfaces [21]. In addition, sol-gel method is also widely used, by preparing inorganic-organic hybrid sols containing fluorine/silicon modifications, which form structures with micro- and nanopores or particles after coating [22]. Ordered rough structures are constructed on the surface of the substrate or coating by templating or chemical/physical etching techniques, followed by modification with low surface energy substances. In addition, spraying or dip-coating functional varnishes containing micro-nano-particles as a surface treatment is a simple process with high commercialization potential, whereas stenciling and etching are less frequently applied in racket mass production.

2.2. Anti-Scratch Coating

The special protective layer on the outer side of a badminton racket frame is primarily designed to enhance its wear resistance. This functional coating effectively maintains the structural stability of the frame by reducing physical damage during daily training and intense matches, thereby ensuring the long-term performance of the sports equipment and providing reliable support for athletes’ on-court performance.

2.2.1. Necessity and Sources of Damage

Badminton is known for its fast pace and fierce confrontation, which includes technical movements such as net rolling, hooking to the corners, etc. are particularly delicate. As shown in Figure 4, during daily training and matches, the racket frame is often damaged due to contact with the ground, retrieving shots, accidental slips, or improper placement, resulting in friction or collisions with rough surfaces, plastic, concrete, or wooden floors. During striking, especially when using slicing or skimming techniques, the strings and the inner edges of the frame, as well as the string hole areas, rapidly generate friction. In net play or when handling defensive shots, the shuttlecock may directly contact the frame, causing scratches or impacts. In doubles matches, accidental collisions with teammates’ or opponents’ rackets may also occur. Additionally, during transportation and storage, friction between the racket and other items in the racket bag can lead to wear. Traditional racket frames, without surface reinforcement, are prone to scratches, abrasions, and paint peeling under external forces. These surface damages not only degrade the aesthetic quality but also create stress concentration areas, which, if accumulated over time, can weaken the frame’s strength and increase the risk of fractures. At the same time, the increased surface roughness interferes with the air flow characteristics, making it difficult to maintain a consistent handling feel when hitting the ball.

2.2.2. Core Functions and Implementation Mechanisms

Protective coatings function through physical and material science principles, with their core being the enhancement of surface hardness [23]. Modified polyurethane, acrylic resin, epoxy resin, and other substrates, combined with nanoparticles such as silica, alumina, and silicon carbide, form composite structures to achieve scratch resistance [24]. Compared to substrate paint or carbon fiber composite materials, the hardness of such coatings is significantly improved, typically measured using pencil hardness or Shore hardness. Their excellent hardness properties effectively resist penetration by sharp objects and rough surfaces, thereby preventing plastic deformation and the formation of scratches [25]. Additionally, high-quality scratch-resistant coatings must not only possess high hardness but also exhibit good toughness and moderate elastic modulus to enhance their resistance to brittle fracture [26]. When impact or high stress is applied, the elastic deformation of the coating absorbs energy, prevents brittle fracture and separation from the substrate, and also evenly distributes surface point loads. Thirdly, by incorporating self-lubricating components such as organic silicon, fluorocarbon compounds, or specialized wax particles, certain coating formulations can effectively reduce the coefficient of friction. These components not only decrease the contact resistance between the coating and surfaces like the ground, strings, or other rackets but also significantly reduce wear and scratches caused by friction [27]. Fourthly, excellent adhesion properties are crucial. The coating must establish strong chemical bonds or physical interlocking with the carbon fiber-based racket frame substrate to withstand external impacts and maintain the durability of the protective effect.

2.3. Vibration Damping Coatings

The shock-absorbing layer of a badminton racket directly enhances the sports experience and technical performance. This mechanism effectively reduces the transmission of harmful vibrations from the racket frame and handle to the athlete’s upper limbs—particularly the wrist, elbow, and shoulder—by absorbing, dissipating, or blocking high-frequency, short-duration impact energy generated during ball strikes [28]. This mechanism not only helps to prevent sports injuries, but also improves clarity of touch and precision of control when hitting the ball, which is essential for maintaining an athlete’s competitive performance [29].

2.3.1. Sources of Vibration, Hazards, and the Necessity of Shock Absorption

Badminton is characterized by frequent, explosive strikes, such as smashes and drop shots, where the contact time between the racket and the shuttlecock is extremely brief—approximately 5 milliseconds. Particularly when hitting outside the sweet spot, significant impact vibrations occur [30]. Long-term exposure to high-intensity vibrations can lead to chronic upper limb injuries such as lateral and medial epicondylitis, which fall under the category of repetitive strain injuries (RSIs). These conditions are closely linked to the physiological harm caused by vibrational energy (as illustrated in Figure 5). Mechanical vibrations may result in muscle fatigue, microtrauma to tendons, stimulation of nerve endings, and localized inflammatory responses [31]. In addition, intense vibration will interfere with tactile perception, weakening the player’s feedback information on the moment of hitting the ball, such as the ball line change, the length of time of touching the ball, and power transmission, which in turn affects his/her ability to accurately judge and adjust in real time the intensity, angle and rotational effect of hitting the ball. This, in turn, affects their capacity to accurately judge and adjust the power, angle, and spin of the shot. During rapid offensive-defensive transitions or delicate net play, uncontrolled minor tremors in the racket face may occur, compromising shot stability and reducing placement accuracy. Persistent arm discomfort or numbness not only increases psychological stress but also accelerates fatigue, ultimately affecting focus and technical performance in later stages of matches or during high-intensity training [32]. To safeguard athletes’ health, ensure consistency in training and competition, and enhance the precision and tactile sensitivity of technical movements, implementing effective shock absorption measures is particularly critical. Beyond racket frame materials, structural design, and handle systems, shock-absorbing coatings serve as a supplementary solution, with their energy-dissipating functionality prominently demonstrated in areas such as the T-joint of the throat, the inner edge of the head, the three-way junction, and even the entire surface.

2.3.2. Vibration Damping Mechanism and Coating Material Technology

The core principle of vibration-damping coatings lies in utilizing the viscoelastic properties of materials—characteristics that combine both viscosity and elasticity—to achieve energy conversion and dissipation [33] (as shown in Figure 6). This mechanism, known as viscoelastic dissipation, is the key to the coating’s vibration-damping function [18]. Typically, modified polymers are used as the base materials, including polyurethane, acrylates, silicone, butyl rubber, and composites with special additives [34]. When these materials are subjected to impact or vibration, their deformation lags behind the applied stress, exhibiting a pronounced hysteresis effect. During deformation, internal macromolecular chains or filler particles within the material rub against each other, converting mechanical vibrational energy into heat for absorption rather than transmitting it outward entirely. CLD (constrained layer damping) serves as an efficient structural design method to effectively suppress vibrations [35]. The racket structure primarily consists of three layers: the base layer uses carbon fiber composite as the frame substrate; the middle layer features a high-performance viscoelastic damping coating for vibration reduction; and the outermost layer is a rigid surface coating or the frame’s structural layer, acting as a constraint. Vibration in the base layer induces bending, forcing the intermediate viscoelastic material to undergo shear deformation, efficiently converting kinetic energy into heat. By applying a thick viscoelastic coating to the outer surface of the frame, such as a rubber layer in the throat area, a free-layer damping effect is achieved. This mechanism leverages coating deformation caused by vibration to dissipate energy through internal friction [36]. Furthermore, incorporating specific functional fillers into the polymer matrix can effectively optimize damping properties. Layered fillers like mica and graphene enhance energy dissipation performance by expanding contact surfaces. High-specific-surface-area materials such as carbon nanotubes and nanoclay not only strengthen interactions between molecular chains but may also create additional energy dissipation pathways. In addition, hollow microspheres achieve effective energy absorption by virtue of their compressible properties.

2.4. Strength-Enhancing Coatings

Special functional coatings are often applied to the surface of the badminton CFRP frame or between the fibre layers to enhance strength. This technology aims to overcome the limitations of traditional coatings, which are primarily decorative and protective, by optimizing the interfacial bonding between fibers and the matrix, repairing microscopic defects in the matrix, and incorporating reinforcing phases. These improvements significantly boost the static mechanical properties and dynamic impact resistance of the racket frame, such as fracture and collapse resistance. As a result, the racket achieves higher structural stability and design flexibility, enabling features like slimmer frames and more advanced string hole designs, which contribute to more stable and aggressive shot performance.

2.4.1. Background of Strength Requirements

To enhance badminton racket performance, contemporary designs emphasize lightweight construction, rebound efficiency, and handling, often achieved through high-modulus carbon materials and innovative frame structures, such as aerodynamic frames and slim profiles. However, these design trends also introduce structural strength challenges, particularly in areas like string holes, T-joints, frame corners, and thinner sections, where stress concentrations are significantly heightened. High-intensity hitting actions—such as string tensions exceeding 30 pounds, smashes with speeds over 400 km/h, off-center hits (especially near the frame edges), as well as collisions in doubles play and accidental drops—can generate substantial instantaneous impact forces. Repeated hitting loads, particularly when striking outside the optimal sweet spot, can induce micro-damage within the material, gradually accumulating and leading to fatigue failure. While the mechanical properties of carbon fiber reinforced composites largely depend on the high-strength fibers, the epoxy resin matrix exhibits relatively weak strength, stiffness, and toughness, and the fiber-matrix interface often represents a potential weak point. Existing protective coatings struggle to significantly enhance the bonding strength between the substrate and the interface. To overcome the strength limitations of lightweight structures, extend racket lifespan—especially under high-intensity play and high string tensions—reduce breakage risks, and ensure player safety and smooth gameplay, it is imperative to develop surface treatment technologies that actively optimize the strength and toughness of frame materials.

2.4.2. Strengthening Mechanisms and Coating Technology Approaches

The optimization of racket frame mechanical properties relies on the enhancement in coating strength, with mechanisms encompassing interface toughening and reinforcement [37]. On carbon fiber or cured substrate surfaces, treatment is performed by applying a primer coating containing components such as silane or titanate. These coupling agent molecules form chemical bonds with the fiber surface at one end while achieving compatibility or reaction with the resin matrix or subsequent coatings at the other end, thereby significantly improving the interfacial bonding strength (IFSS) between the fiber and matrix or between the coating and matrix [38]. By enhancing interfacial energy transfer, interface delamination can be delayed, while simultaneously improving the interlaminar shear strength and impact resistance of the composite material. Through the use of nanomaterials such as carbon nanotubes, graphene, and functional nanoparticles, nanoscale treatment is applied to the fiber surface or interfacial region. This modification not only strengthens mechanical interlocking and chemical bonding due to their ultra-high specific surface area and nanoscale properties but also effectively suppresses crack propagation through the energy absorption capabilities of the nanoparticles themselves [39]. By uniformly dispersing reinforcing phases such as nano-silica, clay, carbon nanotubes, and graphene into the resin matrix, nanoscale composite technology is employed for interlayer impregnation or coating treatment. This process not only reinforces the matrix but also repairs microscopic defects. The pinning effect of nanoparticles can effectively inhibit the initiation and propagation of microcracks within the matrix [40]. Through mechanisms such as crack path deflection and bridging, cracks are forced to change direction or bypass particles, thereby increasing energy dissipation. Using in situ polymerization or infiltration processes, specific coating formulations can penetrate micropores or cracks on the substrate surface, achieving a “filling” and reinforcing effect after curing. Simultaneously, the matrix itself is strengthened, significantly improving the modulus, strength, and toughness of the resin, particularly the fracture toughness K1c. In stress concentration areas such as string holes and T-joints, localized application of high-toughness resin layers incorporating rubber particles, thermoplastic microparticles, or specific toughening components can achieve stress dispersion and toughness enhancement [41]. Through energy dissipation mechanisms such as crazing, shear yielding, and cavitation, the toughening phase effectively absorbs impact energy, inhibiting rapid crack propagation and thereby substantially improving damage resistance in specific regions. Additionally, functional gradient coating technology is employed, where the composition or structure of the coating gradually transitions from the matrix to the surface, optimizing stress field distribution and reducing interfacial stress gradients [42]. Advanced continuous reinforcement techniques are also utilized, where high-strength nanofibers or whiskers are oriented or randomly distributed within the coating, serving as direct load-bearing units to significantly enhance reinforcement effects.

3. Enhancement in Badminton Racket Performance by Coatings

The surface of a badminton racket was divided into six regions in a study (Figure 7a). Regions 1 and 2 almost covered the sweet spot and were located in the upper and lower parts of the sweet spot, respectively. The remaining regions 3, 4, 5 and 6 were non-sweet areas. Figure 7b indicates that the original badminton wires are insulated. Two identical masking plates are placed on the surface of the badminton string. The mask plates are laser cut from an acrylic sheet. The mask plates were fixed symmetrically at the top and bottom and sprayed with metallic conductive silver paint. After spraying, the mask plates were removed and left to air-dry for 10 h; thus, badminton strings with metallic electrodes were obtained. Under the scanning electron microscope to observe a single badminton thread before and after coating with conductive paint. The internal structure of the badminton thread and the difference in external morphology before and after the application of conductive paint can be clearly observed. Due to the weak rigidity of the badminton thread, its cross-section is not a regular circle. In addition, imaging showed that after spraying, the surface of the badminton string was coated with a metallic conductive paint with a thickness of 14 μm (Figure 7c). Conductive silver particles were applied to the string as conductive electrodes. To assess the effect of the 14 μm thin metallic electrode layer on the elasticity of the badminton string, the modulus of the string before and after electrode plating was experimentally measured (Figure 7). The results showed that the modulus remained almost unchanged, indicating that the thin electrode layer did not significantly affect the string elasticity or stroke quality. Figure 7d shows that when a badminton ball comes into contact with a string coated with a metallic silver electrode, two different materials rub against each other and the interaction between their atoms results in the transfer of electrons. One of the materials loses electrons (positively charged) while the other material gains these electrons (negatively charged). When charge separation occurs in a material, a voltage difference occurs between the electrodes, resulting in a potential difference [29].

3.1. Functional Coatings’ Systematic Enhancement in Badminton Racket Durability and Damage Resistance

As high-end sports equipment, the durability and damage resistance of badminton rackets have a decisive impact on players’ daily training, competition safety, equipment cost effectiveness, and sustained competitive performance [43]. As a key technology in sports equipment, coating processes have evolved from their initial aesthetic function to become a crucial support for enhancing racket performance. This study thoroughly examines the strengthening effects of surface treatment technologies on the damage resistance of badminton rackets from multiple perspectives, as well as their significant role in extending service life, providing reliable equipment support for athletes’ competitive performance.

3.1.1. Core Mechanisms and Synergistic Effects of Coatings in Enhancing Durability and Damage Resistance

A multi-level protection and reinforcement system is constructed through various functional coatings based on principles of physics, chemistry, and material science. Among them, the surface protective layer effectively resists external physical wear and chemical corrosion, while the anti-scratch coating achieves ultra-high hardness through nanocomposite technology, coupled with low friction coefficient and exceptional toughness [44]. This enhances surface damage resistance, effectively countering ground friction, string abrasion, and accidental impacts, preventing wear during transportation and storage, and reducing scratches, abrasions, and paint peeling [45]. It maintains aerodynamic performance, protects underlying structures, avoids stress concentration, and preserves aesthetic appearance. As the first line of defense against daily wear, superhydrophobic coatings play a critical role. By combining micro-nano rough surfaces with low-surface-energy chemicals (Cassie-Baxter state), this design significantly enhances anti-fouling and self-cleaning properties, effectively preventing contaminants such as sweat, dust, and oil from adhering and accumulating on the racket frame [46]. This mechanism not only reduces the potential impact of dirt on underlying coating performance but also mitigates the risk of coating aging or substrate corrosion caused by prolonged exposure to corrosive substances like sweat salts and cleaning agents, particularly in humid environments or under improper cleaning conditions. Through the introduction of coupling agents and nanoparticles, the interfacial bonding between fibers and resin is strengthened, while rubber toughening agents improve the matrix material, effectively repairing micro-defects and significantly enhancing the overall strength and toughness of the material. Strengthening internal damage resistance is crucial, with notable improvements in static strength—including tensile, compressive, and flexural strength—enabling effective resistance to high-tension stringing and powerful strokes [47]. In terms of dynamic toughness, enhanced compression-after-impact (CAI) strength and fracture toughness (K1c) help withstand impact loads from off-center hits and accidental collisions. Fatigue resistance, manifested in the suppression of micro-crack initiation and propagation under sustained impact loads [48], significantly reduces structural failures such as frame fractures, collapses, and string hole tears, serving as a critical support for extreme loads and prolonged fatigue. An innovative design achieves a lightweight yet high-strength structure. Through an interfacial energy regulation layer, internal and external impact transmission is effectively mitigated, utilizing vibration-damping coating technology and viscoelastic materials to absorb vibrational energy, combined with constrained layer damping (CLD) architecture [49]. Although its primary function is to enhance user comfort, its ability to absorb high-frequency impact energy effectively reduces the accumulation of micro-damage caused by shockwave propagation in the frame material [50]. This is particularly beneficial for the long-term integrity of stress-concentration areas such as string holes and T-joints. Additionally, it provides a certain degree of cushioning against low-frequency, high-impact events like accidental drops.

3.1.2. Synergistic Effects and the Value of Multi-Layer Coating Systems

Modern high-end badminton rackets commonly employ a multi-layer composite coating system, where each layer does not function in isolation but rather produces significant synergistic effects, collectively enhancing overall durability and damage resistance:

Hierarchical protection: the outer layer, such as scratch-resistant and superhydrophobic coatings, resists environmental erosion and surface wear; the middle layer, such as shock absorption, enhances strength, manages energy transfer, and reinforces the structure; the underlying layer, such as interface enhancement, ensures a strong bond between the coating and the substrate [51]. This forms a complementary in-depth defense system. For example, strength-enhancing coatings improve the substrate’s resistance to fracture, while scratch-resistant coatings protect its surface from scratches that could initiate cracks; shock-absorbing coatings partially dissipate energy, potentially reducing dynamic loads transmitted to the reinforced structure [52]. Performance balance is achieved through careful design of materials and thickness for each layer, optimizing the trade-offs between wear resistance, toughness enhancement, shock absorption, stiffness improvement, and weight control. Extending overall lifespan, the combined action of these protective layers effectively delays the entire degradation process of the racket, from surface wear to performance decline and ultimately structural failure [53].

3.2. Optimization Effect of Functional Coatings on Badminton Racket Elasticity and Hitting Performance

The “elasticity” of a badminton racket is not a singular characteristic but rather its ability to store and release energy during impact. This property directly influences ball speed, rebound characteristics, and the athlete’s perception of power transfer [4]. Meanwhile, the “hitting effect” is comprehensively manifested in ball speed, the stability of flight trajectory, the precision of spin control, and the accuracy of landing placement. Although racket frame elasticity is primarily determined by carbon fiber modulus, structural design, and shaft stiffness, functional coatings can still refine and systematically enhance hitting effects through specific mechanisms.

3.2.1. Core Mechanism: How Coatings Intervene in the Energy Transfer Chain

By toughening the resin matrix with nanoparticles and strengthening the interfacial bonding between fibers and the matrix, the bending and torsional performance of the racket frame in thin-walled areas and high-stress regions can be significantly improved, thereby effectively enhancing the overall structural rigidity and stability [54]. A rigid frame exhibits minimal deformation during impact, particularly evident in smashes and clears. This characteristic reduces energy loss due to deformation, allowing more impact force to be utilized for ball acceleration and deformation. Consequently, power transfer efficiency is improved, resulting in more consistent ball speed. To ensure stable performance in the hitting zone, enhanced rigidity enables uniform distribution of rebound force across the entire effective area, effectively preventing edge collapse caused by frame deformation. This reduces energy loss, expands the effective hitting range, and improves accuracy in off-center hits [55]. To withstand tensions exceeding 30 pounds, the frame must possess exceptional toughness. Specialized reinforcement coating technology ensures this, not only providing quicker feedback during impact but also significantly reducing string bed deformation, thereby enhancing control precision. By improving damping control and energy conduction, vibration-damping coatings are applied to critical areas such as the T-joint at the throat and the grommet holes. Their primary function is to efficiently dissipate high-frequency vibration impacts [56]. Hitting performance is notably influenced by signal purification. By eliminating harmful high-frequency vibrations, players can more acutely perceive key information during ball-string contact, including dwell time, linear force transfer, and sweet spot sensation [57]. Removing interference signals makes operational feedback clearer and more realistic, providing a physiological basis for accurately adjusting shot power, direction, spin, and placement. This clarity is particularly crucial for delicate maneuvers like net drops and cross-court flicks [58]. The primary function of vibration-damping coatings is to convert vibrational energy into heat, thereby reducing ineffective vibrations. Although this process occurs after impact, its core purpose is to protect players and enhance feel rather than directly increase ball speed. Theoretically, the coating can dissipate a small portion of energy that might otherwise transform into harmful vibrations, but this fraction is negligible and has almost no effect on ball speed. By optimizing grip feel, it indirectly improves control precision and power confidence. Maintaining operational stability, reducing frame flutter and hand numbness, ensures consistent face trajectory during high-speed continuous shots, enhancing accuracy and consistency in shot placement [59]. To ensure long-term stability of the frame surface, dual-protection technology combining scratch resistance and superhydrophobicity is employed. These coatings effectively prevent wear, oxidation, and pollutant erosion, preserving the frame’s original aerodynamic performance and surface integrity. In terms of hitting performance, a smooth and undamaged surface ensures stable drag coefficients, aligning with design expectations. While individual scratches have limited impact on overall performance, extensive damage or dirt accumulation can disrupt airflow, slightly increasing swing resistance and affecting swing speed [60]. In elite competition, where milliseconds determine outcomes, maintaining fast swings effectively improves shot accuracy and offensive power. The protective coatings ensure long-term stability of the racket’s aerodynamic performance. They maintain surface stability and predictability, preventing degradation due to wear or contamination [61]. Such degradation could not only affect feel and friction but also alter interactions between the frame, air, and ball, thereby interfering with vibration transmission characteristics and introducing unpredictable feel variations.

3.2.2. Quantitative Understanding and Boundaries of Coating Effects

As a secondary yet crucial optimization aspect, the elastic performance of the racket frame is primarily determined by the modulus grade of the carbon fiber, such as High modulus grade (HM) and Ultra-high modulus grade (UHM) grades. Additionally, structural designs like the stiffness of box frames and the swing speed of aerodynamic frames, as well as the flexibility of the shaft, play significant roles [62]. Different string specifications, tension strengths, and weaving techniques also contribute. The function of the coating lies in enhancing structural stability, improving energy transfer efficiency, ensuring surface properties, and thereby precisely adjusting hitting performance while providing stable support. Although its role is not directly dominant, it holds systematic auxiliary value. The coating’s improvement of elasticity does not directly enhance the frame’s energy storage but reduces deformation losses by increasing structural rigidity, thereby indirectly optimizing the efficiency and stability of elastic output. Furthermore, damping coatings improve the feel, allowing athletes to more fully utilize the racket’s elastic performance [63]. Damping coatings significantly enhance the clarity of feel, an effect particularly prominent among professional athletes. The strength improvement brought by rigidity-enhancing coatings and the performance stability maintained by protective coatings are mainly reflected in the consistency during long-term use and reliability under extreme conditions.

3.3. The Role of Functional Coatings in Reducing Air Resistance and Enhancing Swing Speed

The fast pace and high-intensity competition in badminton determine the core role of swing speed in improving hitting effectiveness and securing high-point advantages. Air resistance has a direct impact on swing speed [64]. In the field of sports equipment, the application of surface treatment technology focuses on improving the physical characteristics of the racket frame by reducing air resistance to enhance its aerodynamic performance [65]. This treatment not only helps increase swing speed but also maintains equipment stability during high-intensity matches [66]. However, the effectiveness of this technology is constrained by various factors, and its application must consider specific conditions and limitations.

3.3.1. Sources of Air Resistance and Core Determinants of Swing Speed

In the aerodynamic drag experienced by a badminton racket, the pressure difference effect dominates, accounting for approximately 70%–85% of the total resistance. This resistance arises from the air pressure difference between the front and back sides of the racket frame, and its intensity is closely related to the cross-sectional shape of the frame [67]. Taking the box-frame structure as an example, while it provides excellent hitting stability, it significantly increases aerodynamic drag. The streamlined aero-frame, with its sharply angled cross-section, effectively guides smooth airflow separation, thereby substantially reducing pressure difference resistance, making it the mainstream solution for improving swing speed [68]. Hybrid frame designs strike a balance between aerodynamics and stability. The frictional resistance caused by shear forces on the frame surface due to air viscosity, although accounting for only 15%–30% of the total resistance, is more significantly influenced by surface characteristics. In racket design, the frame structure is the decisive factor [69]. The aero-frame, with its improved cross-section, fundamentally alters airflow distribution, significantly reducing pressure difference-induced drag. Additionally, the mass and distribution of the frame are crucial: a lighter frame combined with an ideal balance point—while a head-heavy design can enhance swing inertia, it may reduce swing speed; conversely, a head-light design may increase swing speed but weaken hitting power, thereby affecting acceleration performance. Among the key elements of sports performance, strength and technical skill constitute the primary driving factors, directly limiting the maximum swing speed. Within existing structural designs, surface characteristics can only achieve minor improvements by adjusting the friction coefficient and airflow separation zones, with their impact significantly lower than these core factors.

3.3.2. Core Mechanisms and Efficacy of Functional Coatings in Reducing Air Resistance

By improving surface properties, coatings can regulate frictional resistance and local fluid dynamics, with the key being to reduce roughness and maintain smoothness. The primary function of this protective layer is to provide exceptional hardness and wear resistance, effectively preventing scratches, abrasions, and surface roughening caused by ground friction and string wear during daily use. In fluid dynamics, surface smoothness directly affects the velocity distribution of the boundary layer, thereby altering the magnitude of frictional resistance [70]. Compared to a brand-new frame, a frame with noticeable wear marks can significantly increase frictional resistance. By employing anti-scratch treatment technology, surface roughness can be effectively controlled, keeping frictional resistance within design standards [71]. Notably, even under extremely smooth conditions, the proportion of frictional resistance in the total drag remains limited, and its actual impact on overall resistance is insignificant. In terms of swing speed control, the focus is on maintaining stability rather than achieving substantial improvements. By minimizing unexpected speed reductions caused by surface wear, especially after prolonged use, performance can be effectively sustained. The mechanism of superhydrophobic coatings involves microstructures and the trapped air layer, which theoretically can alter the flow state of the boundary layer, promote the expansion of the laminar boundary layer, and delay the transition to turbulence, thereby reducing the frictional resistance caused by the turbulent boundary layer [72]. The position of local airflow separation points may shift due to subtle adjustments in microstructure. In terms of drag reduction, the effect is pronounced in water but negligible in air; superhydrophobic drag reduction technology is highly effective in high-viscosity water environments but has minimal impact in low-viscosity air. Within the actual speed range of a badminton swing, its drag reduction effect is typically less than 1%, far below measurement errors and individual variations. Due to the fragility of superhydrophobic materials, maintaining expected performance in practical applications is challenging, resulting in limited durability.

4. The Impact of Functional Coatings on Badminton Players’ Sports Performance

4.1. Player Control and Comfort

Functional coatings have multidimensional effects on the control and comfort of badminton players (as shown in

Table 2. Impact of Different Coatings on Badminton Racket Performance Enhancement.

Coating Types	Control Influence Mechanism	Performance Correlation
Shock-Absorbing Coating	Suppressing 100–500 Hz high-frequency vibrations enhances proprioceptive clarity	Success rate of net shots improvement
Anti-scratch coating	Maintaining constant friction coefficient ensures spin control	Reduced error range in slice drop shot placement
Strength-enhancing coating	Reducing frame deformation (≤0.8 mm) improves power transmission linearity.	Narrowing the range of fluctuations in the initial velocity of the kill shot

). Although scratch-resistant coatings do not directly influence physical indicators during play, such as rebound efficiency and sweet spot location, their protective function plays a crucial role in maintaining equipment performance and athletes’ competitive levels. By preserving the structural integrity of the racket frame, these coatings effectively prevent the expansion of surface damage, avoiding cumulative micro-damage that could lead to reduced fatigue strength or sudden fractures in the frame. This ensures player safety and minimizes the risk of equipment failure during matches [73]. A structurally intact racket guarantees efficient power transfer and precise control during shots. This not only extends the lifespan of sports equipment but also significantly reduces the risk of premature disposal due to cosmetic wear and surface damage. For professional athletes with high training intensity, this helps save costs while ensuring stable performance over long-term use, thereby promoting the standardization of technical movements [74]. To maintain stable aerodynamic performance of the racket frame, the surface must remain smooth and undamaged, preserving designed characteristics such as drag coefficients. While individual scratches may have minimal impact, extensive or deep surface roughness could slightly increase swing resistance, creating subtle differences in high-speed rallies [75]. The integrity of the racket’s surface coating directly affects the stability of tactile feedback during play. When the coating peels or becomes damaged, vibration transmission becomes uneven, potentially producing abnormal sounds that interfere with a player’s assessment of shot quality. Additionally, from a psychological perspective, well-maintained equipment positively influences players who value gear, boosting their confidence and competitive mindset [76].

The vibration-damping coating plays multiple positive roles in sports performance by suppressing the transmission of harmful vibrations, particularly in injury prevention and health maintenance. It significantly reduces the vibration load on the arm, especially the elbow, effectively preventing and alleviating the occurrence and aggravation of chronic injuries such as tennis elbow. This ensures athletes can maintain healthy training and competition conditions over the long term [77]. Physical well-being is a crucial prerequisite for sustaining high-level competitive performance. By filtering out high-frequency noise vibrations, athletes can more keenly perceive critical information during ball contact, including sweet spot positioning, power transmission, and ball dwell time—core tactile elements [78]. These enhancements in sensory perception are decisive for precisely controlling shot power, spin angle, flight trajectory, and landing position, proving particularly vital in high-level exchanges involving delicate techniques like net drops and slice shots. The coating improves shot accuracy and controllability while reducing handle vibration and hand fatigue, ensuring players can more precisely manage racket angles and motion trajectories during rapid consecutive strikes or powerful swings. This enhances shot consistency and landing precision [79]. By alleviating arm discomfort, it effectively delays the accumulation of muscle and neural fatigue, helping athletes maintain better focus and technical precision during late-game scenarios or prolonged training sessions. Additionally, the comfortable grip and arm protection not only boost athletes’ confidence but also allow them to execute forceful shots—especially smashes—with greater freedom, without concerns about vibration-induced discomfort or potential injuries [80]. As a critical performance element on badminton rackets, vibration-damping materials hold significant importance for sports experience, health protection, and competitive enhancement. This coating utilizes the energy absorption principle of viscoelastic media, particularly through constrained-layer damping structural design, markedly reducing the transmission of harmful vibrations to the arm during impact. It delivers notable positive effects across multiple dimensions, including sports protection, shot feedback sensitivity, operational stability, and precise control.

Although the effect of reinforcement coatings is less pronounced than that of damping coatings, their role in structural support and performance potential cannot be overlooked [81]. In high-intensity matches, stiffer and less deformable racket frames facilitate better power transfer, particularly during high-tension stringing and forceful shots such as smashes and clears. This design minimizes energy loss caused by frame deformation, thereby improving power transmission efficiency and the stability of rebound performance. High-tension stringing enhances shot precision and feedback while imposing greater demands on frame strength, directly influencing ball speed and power performance [82]. Elite athletes benefit from precise control enabled by reinforcement coating technology, allowing rackets to withstand tensions exceeding 30–35 lbs. By optimizing frame design and employing high-strength materials, frames become slimmer, reducing air resistance and increasing swing speed. Additionally, open string hole layouts expand the sweet spot and enhance ball feel. Thinner frame walls further reduce weight, with these innovations significantly improving aerodynamic performance, maneuverability, and shot power—all critical factors for athletic performance. By drastically reducing the likelihood of fractures, these coatings ensure both player safety and uninterrupted competition, representing their core value. They effectively mitigate frame damage caused by accidental impacts, off-center smashes, high tension, or material aging. This advancement not only eliminates the risk of injury from flying debris but also maintains smooth training and competition, preventing unexpected losses due to equipment failure at critical moments [83]. Durability is key to sustained performance. Enhancing a racket’s fatigue and damage resistance ensures structural stability during prolonged high-intensity use, reducing costs for athletes while maintaining consistent equipment performance. High-strength racket designs provide a psychological advantage during extreme power shots or defensive plays, freeing players from concerns about frame damage. This reinforcement coating technology marks a leap from traditional “passive protection” to “active strengthening” in badminton racket coatings. By optimizing fiber-matrix interfaces, enhancing matrix toughness, repairing micro-defects, and incorporating nano-reinforcements, the technology significantly improves static strength, impact resistance, and durability. As the cornerstone of modern badminton racket innovation, this intrinsic reinforcement mechanism achieves extreme lightweighting while enabling ultra-high tension and breakthrough structural designs, ensuring exceptional stability during play [84]. This technological advancement significantly boosts athletic performance by: enhancing power transfer efficiency, supporting high-tension stringing, optimizing aerodynamics and control, and fundamentally reducing equipment failure rates—providing safety for players and ensuring smooth competition [85].

4.2. Potential and Indirect Effects on Sports Performance

The performance enhancement of sports equipment does not directly stem from superhydrophobic coatings; their role lies more in equipment maintenance and user experience optimization (as shown in

Table 3. Performance Enhancement of Different Coating Combinations.

Coating Combinations	Ball Control Stability	Physiological Fatigue Effects	Applicable Scenarios
Scratch-resistant + Shock Absorption	Enhancement	Extension	Multi-shot offense and defense
Enhanced strength + superhydrophobic	Improvement	Extension	High humidity environment
Full-function multi-layer coating	Enhancement	Extension	Major Events

). This technology effectively maintains grip comfort and control precision by preventing sweat accumulation and dripping in critical areas of the racket frame, particularly near the handle. When combined with anti-slip devices or towel grips, and by ensuring the frame remains dry, such coatings can consistently preserve a dry state between the palm and handle, increasing friction coefficients and thereby reducing the likelihood of slippage—especially during prolonged matches or intense rallies [86]. Through its self-cleaning function, the coating effectively prevents dirt buildup on surfaces with anti-scratch, shock absorption, and aerodynamic coatings, ensuring these critical layers maintain their core functionalities—such as scratch resistance, vibration damping, and drag reduction—throughout the racket’s usage, indirectly enhancing sports performance [87]. Additionally, it significantly reduces stain retention, keeping the racket looking new, boosting user satisfaction, and prolonging both the aesthetic appeal and service life of the equipment. By minimizing the contact duration of corrosive substances like sweat and cleaning residues with the racket’s surface or substrate, it effectively slows material degradation, thereby improving overall durability [83]. This design not only simplifies daily maintenance—requiring only rainwater rinsing for cleaning—but also substantially reduces the time and effort athletes spend on racket upkeep, allowing them to focus more on training and competition. Its advantages in waterproofing and stain resistance are particularly pronounced in specific usage environments, such as poorly ventilated high-humidity venues or outdoor recreational badminton activities. Among functional coatings for badminton rackets, superhydrophobic coatings demonstrate notable application value due to their biomimetic properties. With excellent self-cleaning and water-repellent capabilities, they help keep the frame clean and dry, reducing maintenance demands and ensuring the stability of other coating functionalities, thereby enhancing the racket’s long-term usability. Although current technology limits their effectiveness in reducing swing resistance and poses challenges in mechanical durability, their contributions to improving equipment aesthetics, cleanliness, and adaptability in specific environments remain significant.

4.3. The Enhancing Role of Coating Technology on Competitive Performance

The extent to which competitive performance improves due to coating technology varies with the athlete’s skill level, primarily influenced by technical characteristics, training intensity, physiological responses, and the ability to exploit equipment performance limits, as shown in

Table 4. Differential Coating Performance Needs Across Athlete Levels.

Player Typ	Core Requirements	Coating Technology Solutions	Typical Performance Enhancement Scenarios
Professional players	Ultimate control precision	Thin-layer high-damping shock absorption + nano scratch resistance	Crucial point stability, extreme environment adaptability
Amateur enthusiasts	Comfort first	Thick-layer medium damping vibration reduction	Technical movement fault tolerance rate, fatigue delay
Youth	Injury Protection	Full-frame enhanced strength + high-toughness interface layer	Injury prevention, fundamental movement patterning

. Professional athletes excel in seizing critical points, adapting to extreme conditions, and fully utilizing subtle performance advantages [88]. Elite athletes exhibit highly autonomous technical behaviors and are particularly sensitive to minor equipment changes. This coating, with its exceptional tactile clarity, stable shuttlecock speed performance, and reliable grip in humid conditions, effectively reduces the likelihood of critical errors caused by equipment issues, forming its core value [89]. Professional players can keenly perceive and leverage the subtle advantages brought by high-performance coatings, which often play decisive roles in top-tier competitions. For amateur enthusiasts, this technology not only increases the margin for error in movements and delays fatigue but also enhances the overall experience through improved performance [90]. This group possesses solid technical foundations but tends to lose form during intense rallies or fatigue. The comfort and fatigue relief provided by shock-absorbing layers, along with the reliability and durability ensured by scratch-resistant coatings, significantly enhance the stability and continuity of their technical performance, reducing error rates and extending effective playtime [91]. Young athletes place greater emphasis on the “comfort” and “stability” of coatings, with core benefits including injury prevention, assistance in forming fundamental movements, and cost effectiveness. During the stages of skill acquisition and physical growth, adolescents’ musculoskeletal systems are more vulnerable, and their movements are not yet fully stabilized. The impact energy absorption function of shock-absorbing coatings helps prevent sports injuries like tennis elbow, providing health safeguards for future development. By adopting high-strength surface treatment technologies, the structural stability of equipment is significantly improved [92]. Protective film layers effectively reduce maintenance costs caused by equipment wear. At this stage, the key role of surface treatment lies in ensuring the safety and cost effectiveness of training processes rather than overemphasizing performance limits. Functional coating processes optimize the physical properties of rackets and the human–machine interaction experience, thereby comprehensively enhancing the critical elements of badminton: speed, precision, stability, endurance, and reliability [93]. In competitive sports, the value of coatings manifests diversely across athlete levels. Professional athletes focus on stability improvements and gaining marginal advantages, amateur elites prioritize error tolerance and durability, while youth groups emphasize safety and foundational training. Through innovations like smart-responsive coatings, combined with sports biomechanics and big data analysis, the application prospects for enhancing athletic performance will further expand.

5. Challenges in the Application of Functional Coatings in Badminton Rackets

5.1. Technical Feasibility and Cost Issues

The research value of surface treatment technologies for badminton rackets has garnered significant attention. However, during the transition from laboratory stages to large-scale production and commercial promotion, numerous technical bottlenecks and economic efficiency issues persist. These factors not only limit the widespread adoption and performance limits of the treatment technologies but also have a decisive impact on their scope and effectiveness in enhancing athletic performance.

5.1.1. Core Technical Feasibility Challenges

In the field of coating technology, the “impossible triangle” dilemma of balanced performance persists, with its core lying in the inherent conflicts among high performance, durability, cost effectiveness, and lightweight properties. Overemphasizing the extreme performance of one characteristic often leads to significant drawbacks in other aspects. For instance, ultra-hard anti-scratch coatings, while offering excellent performance and durability, are often limited by excessive brittleness and insufficient toughness, along with the inclusion of expensive nanomaterials that increase coating thickness. On the other hand, broadband high-efficiency vibration-damping coatings, though effective in absorbing vibrations, typically use high-damping materials that are soft, lack wear resistance, and are sensitive to temperature and humidity changes, requiring special fillers that drive up costs. The complexity of nano-dispersion technology leads to a sharp increase in the cost of high-concentration nanoparticles and may impair resin fluidity. The fragility of micro-nano structures poses a core challenge for superhydrophobic coatings, while ultra-tough reinforcement coatings face technical hurdles. In multi-layer coating systems, the physicochemical properties of primers, functional layers, decorative layers, and topcoats—such as thermal expansion coefficients, elastic modulus, adhesion, and curing conditions—must remain harmonized [82]. Mismatches in these properties can lead to defects like interlayer separation, cracks, or bubbles. Particularly, the interfacial bonding strength between functional coatings and carbon fiber composite substrates is critical for long-term stability.

5.1.2. Complexity, Stability, and Scalability of Manufacturing Processes

High-performance coatings, especially those containing nanomaterials or employing CLD designs, demand extremely stringent control over coating uniformity, thickness precision, and curing temperature and time profiles. Achieving stable and consistent large-scale production on complex curved surfaces presents significant challenges. Nanoparticles tend to agglomerate in resin matrices, and achieving their uniform and stable dispersion is key to enhancing the performance of nanocomposite coatings. However, this process faces challenges such as technical complexity, fine-tuned processes, and expensive equipment. Due to increasingly stringent environmental regulations, traditional solvent-based coatings with high VOC emissions are under pressure. To address this, the industry is actively transitioning to greener technologies like water-based, high-solid-content, and UV-curable coatings. Yet, such process innovations often require reformulating designs, upgrading equipment, and may even impact product performance—for example, early water-based coatings may underperform solvent-based products in hardness and water resistance. High-speed production lines struggle to achieve non-destructive real-time monitoring of coating performance, including critical metrics like interfacial adhesion, internal distribution, nanoparticle uniformity, and loss coefficients.

5.1.3. Cost–Benefit Analysis and Key Market Adoption Constraints

The procurement costs of special raw materials such as high-performance resins, modified polyurethane, fluorinated resins, and nano-scale materials remain high. Coupled with the use of efficient coupling agents, functional fillers like hollow microspheres, and specific toughening agents, the overall material expenditure has significantly increased. For instance, high-quality carbon nanotubes are priced far beyond ordinary resins, with the difference reaching several folds. In industrial production, the purity and batch consistency of raw materials are core requirements, directly driving up production costs. Additionally, precision coating technology requires high-precision automated equipment to achieve uniform coating, precise thickness control, and special curing (such as UV LED). These complex processes and equipment investments result in extremely high initial costs. To meet environmental and safety standards, investments in clean rooms and VOC treatment systems are essential. Furthermore, nano-dispersion equipment like high-shear dispersers, ultrasonic devices, and grinding machines incur not only high procurement costs but also significant maintenance expenses. Due to the complexity of the processes, yield rates face severe challenges, with frequent occurrences of defects and rework, further increasing production costs.

5.1.4. Market Positioning and Consumer Acceptance

In the badminton racket market, cost pressures often manifest in product pricing, creating significant price disparities. Professional athletes prioritize performance optimization and are willing to pay a premium, while general users focus more on cost effectiveness and are sensitive to price changes. Amateur consumers pay more attention to the visible features of coatings, such as lightweight, elasticity, and hitting speed, but generally lack sufficient awareness and value assessment of hidden advantages, including durability and structural stability. Market cultivation requires solid empirical evidence. When high-end technologies penetrate mid- to low-end product lines, companies often face multiple challenges in cost control, performance maintenance, and process simplification, which can easily lead to feature reductions or degraded user experiences.

5.2. Environmental Protection and Sustainability

With the increasing global emphasis on environmental protection and sustainable development, the sports equipment manufacturing industry, including the badminton racket sector, is facing unprecedented pressure for green transformation. Functional coatings, as a critical component of racket manufacturing, have environmental impacts throughout their entire life cycle (Life Cycle Assessment, LCA), from raw material acquisition, production, and manufacturing to use, maintenance, and disposal. Driving coating technology toward environmental sustainability is no longer just about fulfilling corporate social responsibility (CSR) and meeting regulatory requirements but has become a strategic core for the long-term healthy development of the industry and enhancing brand value, ultimately serving the sustainable future of sports.

The environmental footprint of raw materials, reliance on petrochemical resources, and the base resins and monomers of traditional coatings, along with solvents, are primarily derived from non-renewable petrochemical products. Their extraction and refining processes are accompanied by high carbon emissions and ecological damage. Risks from harmful additives and nanomaterials, such as certain plasticizers, flame retardants, heavy metal-containing pigments, and some nanomaterials like specific forms of nano-silver or insufficiently studied nanoparticles, may be released during production, use, or disposal, posing potential bioaccumulation and ecotoxicity risks. The long-term environmental impact assessment (Ecotoxicology) of these substances remains incomplete. The use of scarce resources, such as rare metal catalysts or special elements in high-performance coatings, exacerbates resource scarcity pressures. Pollution and energy consumption in the manufacturing process, particularly volatile organic compound (VOC) emissions, represent the most significant environmental challenge for traditional solvent-based coatings. The volatilization of large quantities of organic solvents like toluene, xylene, and ketones during the coating process serves as a major precursor for ozone (O₃) and fine particulate matter (PM2.5), severely polluting the air, endangering worker health, and requiring substantial investment in end-of-pipe treatment facilities. High-energy processes, such as high-temperature curing (e.g., baking tunnels), consume vast amounts of energy, and certain nanomaterial dispersion techniques (e.g., prolonged high-power ultrasonication) are also energy-intensive. If the energy structure relies on fossil fuels, this indirectly leads to high carbon emissions. Wastewater and solid waste, including equipment cleaning and pretreatment processes like degreasing and phosphating, generate chemically contaminated wastewater. Waste coatings, used wipes, and failed filtration materials are classified as hazardous waste, incurring high disposal costs and posing secondary pollution risks. Hidden impacts during product use and maintenance, such as insufficient coating durability leading to premature racket disposal, increase resource consumption and waste generation. Frequent cleaning or the use of strong cleaning agents may also impose environmental burdens, such as wastewater containing phosphorus or surfactants. The potential risk of microplastic release, where coatings may shed microplastic particles during long-term wear or cleaning, entering water and soil systems, is increasingly concerning. Challenges in disposal, particularly the recycling dilemma of composite materials, arise because badminton rackets are primarily made of carbon fiber-reinforced polymer (CFRP) and coated with multiple layers of different materials. This heterogeneous composite structure makes efficient separation and recycling extremely difficult. Currently, the vast majority of discarded rackets (including coatings) end up in landfills or incineration, leading to resource waste and environmental pollution—landfills occupy land and pose potential leaching risks, while incineration may release harmful gases. Coatings hinder recycling, especially thermosetting resins that are difficult to degrade after cross-linking and curing, and may contain chemicals that impede the recycling and reuse of carbon fibers, such as those affecting reprocessing performance. While there are multiple challenges to environmental protection and sustainability, there are also practical products that go along with them, such as the recent water-based formulations specific to green coatings in sports equipment, and linking them more closely together tends to produce better environmental and sustainable results.

6. Summary and Future Outlook

6.1. Summary

As a crucial medium connecting advanced material science with sports biomechanic efficacy, the functional coatings on badminton rackets have transcended the traditional limitations of protection and aesthetics. This study marks the first comprehensive review of five key functional coating systems for badminton rackets—waterproof, scratch-resistant, shock-absorbing, strength-enhancing, and superhydrophobic coatings—categorizing their mechanisms and systematic impact on sports performance, thereby filling the interdisciplinary theoretical gap in this field. This research delves into the core mechanisms of various coatings: hydrophobic and superhydrophobic surfaces, leveraging their micro-rough structures and low surface energy properties (Cassie-Baxter state), and establishing protective barriers and self-cleaning functions. Nanocomposite technology enhances surface characteristics, not only improving coating hardness and toughness but also significantly reducing friction coefficients. Viscoelastic materials, due to their hysteresis effect, effectively absorb high-frequency impacts, achieving shock absorption. Furthermore, through interface toughening, matrix reinforcement, and repair of micro-defects, the static strength and dynamic impact resistance of coatings are markedly improved. Functional coatings employ a multi-level synergistic mechanism to comprehensively enhance racket performance. By constructing a three-dimensional protective network spanning surface protection, structural reinforcement, and energy regulation, the wear resistance, corrosion resistance, environmental erosion resistance, and impact resistance of the equipment are significantly enhanced, ensuring safety and extending service life. The application of reinforced frame coatings not only effectively suppresses racket deformation but also improves energy transfer efficiency and the stability of shot speed. Meanwhile, the introduction of shock-absorbing coatings substantially mitigates the adverse effects of high-frequency vibrations, resulting in more precise tactile feedback. This not only increases the success rate of net shots but also significantly enhances the accuracy of delicate techniques like slice drops. By maintaining a consistent friction coefficient, scratch-resistant coatings improve the reliability of spin control. This coating synergy ensures the aerodynamic characteristics and surface performance of the racket frame remain stable over long-term use. Leveraging coating technology, the stability of physical output and the efficiency of human–racket interaction are optimized, providing subtle competitive advantages. The extent of improvement in core metrics varies by athlete level: professional players excel in leveraging stability during critical points, environmental adaptability, and nuanced advantages, and advanced amateurs benefit from technical fault tolerance and fatigue resistance, while youth players focus on injury prevention and fundamental technique standardization. By integrating multidisciplinary knowledge from material science, mechanics, fluid dynamics, and sports biomechanics, this study constructs a holistic theoretical model of “coating structure—racket performance—athlete experience—competitive output,” demonstrating significant interdisciplinary value.

6.2. Future Prospects

In the enhancement of badminton racket performance and athletic performance, functional coating technology has made significant progress, but its future development and application still present multiple challenges and opportunities. The research focus should shift toward intelligent and responsive coatings, developing smart coatings capable of sensing and adapting to environmental changes or hitting conditions. For instance, temperature-sensitive or humidity-sensitive polymer coatings could dynamically adjust friction coefficients or damping properties, while piezoelectric or triboelectric material coatings could harvest impact energy to enable self-powered sensing functions. A racket performance optimization system based on smart sensing and artificial intelligence integrates embedded detection modules, adaptive surface treatment technologies, and machine learning models to achieve personalized dynamic adjustments. This platform centers on digital sports analytics, emphasizing the correlation between coating parameters and professional players’ tactical decision-making. By establishing a high-precision testing system, complex working conditions are simulated, encompassing multi-field coupling effects such as impact, friction, temperature variation, humidity variation, light exposure, and chemical corrosion to evaluate service performance and lifespan. Combining physical principles with big data analytics, a coating durability assessment system is constructed to accurately predict performance changes and service life under harsh conditions. Advanced detection methods are employed to dynamically track microscopic damage under repeated stress, revealing quantitative relationships between microstructural changes and macroscopic performance degradation. As regards promoting eco-friendly production innovation, in the industrialization of environmentally friendly materials, emphasis is placed on advancing low-volatile technologies such as water-based coatings, high-solid-content coatings, and UV-curable coatings for badminton racket applications. Key challenges include bridging the performance gap between water-based systems and conventional solvent-based coatings in terms of hardness, moisture resistance, and curing speed. Simultaneously, efforts are directed toward developing bio-based and biodegradable materials, and exploring the use of renewable resources to produce high-performance resin monomers and additives. To address the recycling challenges of discarded rackets, this study focuses on developing coating systems that can gradually degrade in specific environments or be easily separated from carbon fiber substrates. By refining coating techniques to reduce energy consumption and exploring efficient nanoparticle dispersion and stabilization methods, the manufacturing process is streamlined, minimizing energy usage. Additionally, strategies for the efficient recovery and resource utilization of wastewater, waste solvents, and solid byproducts generated during coating processes are investigated to enable material reuse. By analyzing the biomechanical characteristics of various athletes, their specific coating performance requirements are explored, establishing a “demand-function-structure” correlation model to advance personalized coating design. This approach emphasizes the deep integration of coatings, structure, and user needs, enabling customized development for individuals with different skill levels and playing styles. Through formulation refinement and process optimization, coating thickness and weight are reduced while maintaining performance standards, integrating multiple functionalities to prevent adverse effects on racket weight distribution.