The consumer practice shift of wearing activewear apparel during everyday activities, called athleisure, led to a change in expected comfort and functionality of a key clothing item, such as the sports bra (Dhanapala 2015). For women participating in exercise, breast support is crucial, and consumers regard this feature as the main function of a sports bra (McGhee et al. 2013). Generally, sports bras are designed to provide increased levels of support to a woman’s breasts, often by compression, in order to restrict movement of the breasts during exercise, at the expense of comfort during resting activities (Dhanapala 2015). Although major developments in fiber and textile technologies have been employed to improve sports bra design and its functional properties, the sports bra industry is struggling to offer an adaptable and responsive design, which can support the breasts during high impact sports, such as running, and also feeling comfortable during rest (Burnett et al. 2015).
In the design of functional apparel, the evidence-based methods combined with the creative processes of fashion design frame the traditional user-centered design approach (Watkins and Dunne 2015). However, many of the innovations in textiles and materials with adaptive and responsive properties have been informed by biomimicry, or biomimetics, which is an emerging theoretical design framework “that seeks sustainable solutions by emulating nature’s time-tested patterns and strategies” (Frumkin et al.2011). Biomimetics represents the convergence between biology and engineering, and its applicability to various product design challenges offers opportunities for knowledge transfer between domains, as well as the potential emergence of a new body of knowledge (Cohen and Reich 2016).
Biological systems have been found to offer feasible design analogies to functional apparel design, because they manifest responsive behavior when actuated by environmental factors such as light, moisture, pressure, and motion ( Frumkin et al. 2011). Like the functional hierarchy found in the natural systems, a typical sports bra design has several layers of materials (fiber, yarn, and fabric), constituting inter-related subsystems that react when the wearer moves, sweats, and eventually dries out. Instead of drying out the perspiration of the wearer by using moisture wicking fibers and fabrics, as it is the current design practice, a responsive solution is required to absorb the perspiration back into the system. The moisture- induced changes at the material level should preserve the functional properties of the sports bra, such as breast support and perceived bra comfort, through both dry and wet conditions. This mechanism is defined in this study as “responsive behavior.”
Therefore, the purpose of this experimental study was to design a sports bra that offers responsive behavior when actuated by the perspiration of the wearer, meaning the sports bra maintains its comfort and breast support both during rest (dry conditions), as well as during running exercise (sweaty conditions). The biomimetic design framework was used to guide the sports bra conceptual design phase, while Smart Apparel Design Process (SADP) critical path proposed by McCann (2009) was employed for the prototype development and evaluation. No previous studies were found to apply the emerging biomimetic framework to sports bra design, all the way to prototyping and evaluation. The results of this investigation, conceived via an inter-disciplinary framework, provide an innovative approach to improving the design of a key apparel item for women, the sports bra, aiming at encouraging healthier lifestyles, as well as filling significant knowledge gaps.
Sports bras as functional apparel
Sports bras are an essential piece of sporting equipment, and their main purpose is to support a woman’s breasts as she practices sports or physical activities (McGhee et al. 2013). Burnett et al. (2015) found that continuous and repetitive movement without external breast support can result in breast soreness, pain, and sagging. However, the geometrical complexity of women breasts makes designing sports bras with effective breast support difficult (Bowles et al. 2012). The most common complaint is insufficient breast support, especially among the larger breast sizes, with some designs performing better than others, and efficient breast support in design features is often traded off for comfort (Dhanapala 2015). Moreover, McGhee et al. (2013) found that breast movement and bra discomfort are key barriers to exercise, highlighting the two main user-needs: breast support and bra comfort.
Breast support
Currently, sports bras are generally classified into two main categories: (a) compression and (b) encapsulation bras. Compression designs offer breast support by uniformly pressing both breasts against the chest wall, while encapsulation designs separate the breasts and support them individually (Luk and Yu 2016). Compression sports bras with higher necklines were found to better restrict the upward movement of the breasts (Bowles et al. 2012). Starr et al. (2005) claimed that encapsulation bras are more effective in controlling breast movement than compression bras. Other studies reported no significant differences between the two types of bras regarding their reduction of vertical breast displacement (White et al. 2009; McGhee et al. 2013). However, the reduced number of sport bra designs tested represents a significant limitation of the findings. Sports bras that have a combination of compression and encapsulating features were found efficient in managing breast support for women with large breasts (Morris et al. 2017).
Many other factors, such as bra materials, assembly details, and shoulder strap design were found to influence breast movement and support (Zhou et al. 2013). The shoulder straps are essential to support the mass of the breasts, but they often are perceived to be uncomfortable by causing too much pressure on the shoulders (Mills et al. 2015). Crossing the straps at back was found to prevent them from slipping off the shoulders, and use of inelastic materials for wider straps was more efficient at managing breast displacement (Bowles et al. 2012). A comprehensive review of mostly empirical studies of breast motion, biomechanics, and sports bra designs reported inconsistent findings in terms of most efficient design solutions for managing breast support (Zhou et al. 2013). Moreover, the traditional bra sizing system has shortcomings and is unable to cover a broad range of unique anatomical breast shapes (McGhee et al. 2013). Most studies have assumed that breasts are symmetrical, resulting in potentially misleading design recommendations (Mills et al. 2015).
The key performance variables that distinguish between levels of breast support needed during various sport activities are still unclear, and there is no industry standard to determine the performance of sport bras (Zhou et al. 2013). The types of exercises considered in the breast motion studies are mainly walking, running, jogging, and aerobics, and the breast displacement was found to be the highest in running (McGhee et al. 2013). Therefore, sports bras are designed with specific levels of support or compression, based on the nature of the intended activities or motion: (a) high, (b) medium, or (c) low support (Zhou et al 2013). Burnett et al. (2015) found that each woman has her own comfort tolerance for how much breast support she needs. However, women often prefer to wear a sports bra during most of their daily activities, not just for exercising (Bowles et al. 2012). Therefore, the demand for multifunctional sports bra, which incorporate both, breast support and comfort during various activities, has increased (Dhanapala 2015).
Bra comfort
Lawson and Lorentzen (1990) found that bras that effectively controlled breast displacement scored lower on comfort variable. McGhee et al. (2013) linked breast elevation and compression to increased breast discomfort, and proposed the inclusion of thick foam pads inside encapsulating bra cups. The tightness of the underbust band was reported to be a comfort deterrent for women to wear a sports bra (Chen et al. 2016). While breast comfort is related to breast displacement, velocity and acceleration, Starr et al. (2005) stated that perception of bra support and perception of comfort are multi-dimensional variables that also involve the transport of moisture and air through the fabric.
Fabric selection
The use of fabrics with dynamic moisture properties improve the wearer’s thermal comfort, and sports bras should have good moisture management properties (Tiwari et al. 2013). Therefore, moisture wicking fibers and fabrics are commonly used for sports bras, along with fabrics designed to allow ventilation (Watkins and Dunne 2015).
Innovations in both yarn and manufacturing technologies have elevated knitted fabrics to have comfort qualities that far outweigh those offered by woven fabrics (McCann 2005). Particularly, the use of weft knitted fabrics in activewear has increased due to the demand of stretchable and tight- fitting garments. (Watkins and Dunne 2015). As a garment worn close to the skin, the seams constructing the sports bras have been found to be uncomfortable, therefore seamless knitted designs made with circular knitting machines emerged (Yip and Yu 2006). Seamless circular knitting machines have been the primary technology used for manufacturing compression sport bras, due to achieving uniform compression levels around the body (Tiwari et al. 2013). The addition of spandex yarns in circular knitted fabrics create a compressive fit that is maintained without deformation during the product life (Lau and Yu 2016). Moreover, a major advantage of creating sports bras on circular knitting machines is the ability to create seamless three-dimensional shaping, such as encapsulating breast shaping, as well as engineered compression and ventilation within different areas of the garment (Lau and Yu 2016). Zhou et al. (2013) found that seamless sports bras are not preferred as daily bras, due to their unflattering compression of the breasts, even though they scored highest on comfort.
Moisture management
Many studies reported properties of knitted fabrics made of various fibers and yarns capable of absorbing moisture (Troynikov and Wardiningsih 2011; Tiwari et al. 2013; Venkatraman 2015). Commercial sports bras contain elastane, polyamide, or polyester fibers that are lightweight, easy to wash, dimensionally stable, and dry quickly (Zhou et al. 2013). However, (Cotton Incorporated’s Lifestyle Monitor Lifestyle Monitor 2015) surveyed 1,500 men and women, and around 70% of women said they prefer cotton and cotton blends for activewear, and 81% associate better quality with all-natural fibers. Although polyester or polyamide fibers cannot provide the high-level comfort of cotton, Coolmax®, an enhanced polyester derived fiber, was found to significantly improve moisture wicking and comfort (Venkatraman 2015). Kaplan and Okur (2008) argued that it is necessary to study and use natural fibers in activewear, if they can provide comparable functionality to the ones made of synthetic fibers. Cocona®, a new wicking fiber made from coconut shells, is used in Champion’s Vapor sports bra, and it is claimed to outperform Coolmax® (Lau and Yu 2016).
The structure of the fabric itself can enhance the moisture management properties designed at the fiber and yarn levels (Scott 2015). For example, knitted fabrics made with Teijin’s Fibaliver®, in presence of moisture, change their stitch density to improve air permeability, and then revert to the dry properties in absence of moisture (Lau and Yu 2016). Sarkar et al. (2010) reported on the dimensional changes of hygroscopic yarns when utilized to develop responsive fabric structures. They found that engineered openings in the fabric widen or narrow depending on moisture content, leading to improved air permeability in conditions of high moisture content, similar to body sweating. However, few studies have been investigating the responsive properties of natural fibers as applied to improving the functionality of activewear (Watkins and Dunne 2015).
Both cellulose and protein natural fibers have dynamic moisture absorption properties; fibers increase in volume in the presence of moisture, almost entirely in the radial direction (Scott 2015). Merino wool is an emerging performance fiber, and it has been reported to have properties suitable for activewear, and several seamless knitted sports bra designs are currently on the market made from Smartwool® yarns (Millington and Rippon 2017). Pure Merino wool has been blended with other fibers to regulate moisture absorption, wicking, air circulation and to enhance the comfort of the wearer (Venkatraman 2015). Blending wool with polyester, or wool with bamboo, improved the moisture management properties of the fabrics compared with 100% wool and 100% bamboo fabrics (Troynikov and Wardiningsih 2011). Wool has been found to have better responsive behavior when actuated by moisture than cotton, because wool has approximately a 30% increase in diameter when absorbing moisture, one of the highest out of all natural fibers (Scott 2015; Sarkar et al. 2010).
Moreover, during the selection of fiber and fabric types used for the design of sports bras, it is important to consider the sweat patterns of the wearer (Venkatraman 2015; Watkins and Dunne 2015). For female runners, it was found that the center front area between the breasts accumulates the most sweat (Havenith et al. 2008), and that is where moisture management has to be systematically designed into the details of the fiber, yarn, fabric, and shape of the sports bra. Moreover, researchers have used both objective and subjective measurements to evaluate the moisture management performance of sports bras (Bowles et al. 2012).
Design process for sports bras
Watkins and Dunne (2015) stressed the importance of thorough understanding and framing of the user needs for all design activities. However, sports bras marketplace has experienced a convergence of functionality, comfort, and fashion, highlighting new user needs, and creating new complexities for product developers and designers (Dhanapala 2015). Therefore, various researchers focused on limited target cohorts of sports bra users, with specific anatomy and functional requirements ( Barner and Morris 2016; Morris et al. 2017). Watkins and Dunne (2015) suggested the User Centered Design (UCD) framework as suitable for a wide range of functional clothing designs. The UCD approach leads the designers through five stages: (a) mapping of the exact user needs, via questionnaires, interviews, and focus groups, (b) determination of user goals for the product to be successful, (c) designing of solutions, (d) evaluation of solutions through wear-testing with actual users, and (e) assessment of the solutions (Morris et al. 2017).
However, (Frumkin et al. 2011) argued that there is a growing distinction between designing products using already developed and well-defined technologies, and designing products using new technologies and embedded functions. The efficient integration of a responsive function into textiles cannot be achieved as an added layer, but it has to be considered simultaneously throughout the design development process of the entire product (Watkins and Dunne 2015). McCann (2009) proposed the Smart Apparel Design Process (SADP) framework, as an inclusive guide for the responsive (smart) garment design process, which considers all the challenges that embedded technologies bring to the prototype development. The suggested design critical path through disparate yet interdependent stages, includes the following: (a) identification of end-user needs, (b) textile development, (c) garment development, (d) integration of smart technologies, (e) garment manufacturing, (f) distribution, and (g) end-of-life recycling. Each stage begins before the previous one is finished, and many can overlap (McCann 2009). This systematic design process is currently used in the industry for developing sports bras with embedded biometric monitoring functions.
Although all designs involve creative problem solving, the ideation process is not often included in design process models (Cohen and Rich 2016). Biomimetics, a term defining the process of transferring knowledge from the responsive natural systems into technology, has been a theoretical model that produced significant innovations in the past half of the century (Vincent et al. 2006). Breakthrough innovations often result from functional analogies between different domains, such as biology and functional apparel design (Vincent et al. 2006). However, biomimetic research and its applications to functional apparel design has been done on a case-by-case basis. Cohen and Rich (2011) proposed a multi-disciplinary six steps iterative biomimetic design process: (a) problem definition, (b) biomimetic problem definition, (c) identify analogical source, (d) abstract design solution, (e) transfer solution to biomimetic application, and (f) evaluation and iteration. This sequence of steps, overlapped to SADP framework, created a hybrid design process that better fit the purpose of this study.
Research gaps and questions
Sports bras studies that were reviewed in the previous sections concluded that, despite the existing wide range of styles, manufacturing approaches and design processes employed, there is a significant need for improved sports bra design (Bowles et al. 2012; McGhee et al. 2013; Zhou et al. 2013; Lau and Yu 2016). The increased focus on designing for efficient breast support, resulted in many designs that are uncomfortable and actually deter women from practicing sports (McGhee et al. 2013; Bowles et al. 2012). Moisture management at fiber and fabric levels was found to be related to perceived bra comfort, but no studies investigated the variations in perceived comfort and breast support between dry and sweaty conditions (McCann 2005; Venkatraman 2015). Moreover, no literature was found regarding studies of sports bras that have adaptive, responsive properties. The few examples of responsive sports bras commercially available involve e-textiles in order to monitor biometrics, with bras producing an electronic output to a watch or a phone, and not changing or adapting the fit and comfort functionality of the sports bra itself (McCann 2005). Although biomimetics have been used in enhancing performance of various functional apparel designs, no studies reported on attempts to create a moisture responsive sports bra design using a biomimetic analogy. (Lovel et al. 2006) developed a theoretical proposal for a bra strap design, using biomimetic framework, but without developing a prototype and evaluating the solution.
By addressing the literature gaps mentioned above, the aim of this study was to develop a sports bra that is comfortable and supportive when dry, but, in a biomimetic manner, it can change its material properties to absorb the moisture generated by the wearer during running, to maintain perceived comfort and breast support when wet. In order to achieve this aim of the study, the following three research questions (RQs) were created, reflecting the main stages of the design process: (a) design (RQ1), (b) develop (RQ2), and (c) evaluate (RQ3):