Bra Underwire Customization With 3-D Printing

Abstract

In the current research, we aimed to investigate whether customized 3-D underwires improve bra performance. The first experiment was designed to study whether customized 3-D printed underwires provide significant benefits over conventional wires. Customized 3-D underwires were produced following individual breast root shapes and compared with conventional underwires through wear trials. According to the empirical data, pressure was significantly reduced with the customized underwire, and performance improvement was more evident with wearing sensations of support and comfort. In the second experiment, we varied the length of the customized underwires and observed how the length of underwires influenced bra performance. More pressure was found in the outer region of the longest underwires than the medium-length wires but support and comfort sensations did not have noticeable changes depending on the wire length. As illustrated in this research, advanced 3-D technologies could contribute to product engineering and customization in the apparel industry.

Keywords

bra underwire bra customization 3-D printing

Bra underwires are the second largest cause of discomfort when wearing a bra, following incorrect cup size (McGhee & Steele, 2010). Bra underwires may cause discomfort where the underwire presses on the skin. Localized pressure on breast tissue can cause health issues such as pectoral myalgia (Greenbaum, Heslop, Morris, & Dunn, 2003; Ryan, 2000), hyperplasia of mammary glands (Wang, Chen, & Lin, 2009), and mastitis (Legato & Gerber, 2014). Furthermore, with long-term wear, underwires may become distorted in shape and emerge from the channeling, causing additional health risks such as metal allergies. As an alternative, wireless bras were introduced into the market to reduce underwire pressure and improve comfort during wear (Yuasa, Tachiri, & Fujii, 2018; Zheng, Yu, & Fan, 2009). However, underwires are still considered necessary to support the breasts effectively and are still prevalent in the market (Lee & Hong, 2007; Wang et al., 2009).

Bra comfort may be improved by advancements in design and production technologies such as 3-D body scanning and 3-D printing. There have been several examples of product innovations facilitated by recent technologies in the textile and apparel industries. In the apparel industry, 3-D scanning technology has been adopted to accurately replicate individual body size and its shape (Istook & Hwang, 2001). 3-D printing led to early innovations in haute couture and wearable art and has gradually spread to the general market (Cuzella, 2015). In the shoe industry, 3-D technologies in knitting and printing have been adopted to produce uppers as well as soles (Informa, 2015). More fashion companies are attempting to incorporate 3-D printing into their fabric, garment, and accessory production lines (Brooke, 2013).

The purpose of this study is to investigate whether customized 3-D printed underwires can improve bra performance in a way that increases support and enhances comfort. Thus, customized 3-D printed underwires were developed and compared to conventional underwires in this study. Breast shapes were captured using 3-D body scanning technology, and custom underwire shapes were developed from the body scans. The researchers used 3-D printing technology to develop the custom underwires in shapes that conformed to the unique breast root of each individual, while the conventional underwire was a flat 2-D wire in a standard shape. Furthermore, the researchers developed the custom 3-D printed underwires in three different lengths to determine their impacts on bra support and comfort. Pressure and wearing comfort were evaluated through wear trials and analyzed through statistical tests.

Literature Review

A brassiere primarily functions as an external support for the breast. There are two types of bra products in the market, each with a different functional focus. A fashion bra is worn primarily for aesthetic reasons. This brassiere changes the breast dimensions and serves to alter the bustline into a more attractive shape (Cha, 2012; Inui, Murase, & Tsutsumi, 2012; Jian & Wei, 2007). A sports bra is designed to control breast movement. In particular, it is expected to restrict breast displacement during physical activities (Lawson & Lorentzen, 1990; Zhou, Yu, & Ng, 2013). This restriction is achieved by encapsulating and/or fastening the breasts with an appropriate amount of force (Yan, Gao, Jin, & Tao, 2014).

A typical brassiere consists of six basic components: cup, underwire, gore, wing, fastener, and shoulder strap (Yu, Fan, Ng, & Harlock, 2014). A bra cup covers each breast fully, for two thirds, or for half of the breast, depending on the bra style. A U-shaped underwire is often placed along the lower edge of the bra cup and helps the bra cup encompass the breast better. Locating each bra cup along the under-breast contour, a gore connects two bra cups at the medial side in the center front region. A wing, often called as a band, connects the bra cups to the lateral side across the back and fastens in the center back region by a fastener. Hooks and eyes are the most common type of fasteners (Yip, 2016). Finally, two shoulder straps connect the upper edge of each bra cup to the back band over the shoulder.

To achieve the intended purpose of any kind of brassiere, it is very important to ensure correct breast size measurement and bra fit (Yu et al., 2014). However, according to Wood, Cameron, and Fitzgerald (2008), there are considerable differences in bra size estimates when breasts are measured by experts as compared to general consumers. This discrepancy was often as much as three cup sizes, and large-breasted women had a greater tendency to underestimate their breast size. When a brassiere does not fit correctly, it does not support the breasts and thus causes much discomfort to the wearer (Lawson & Lorentzen, 1990; White, Scurr, & Hedger, 2011). It has been a long-standing challenge for both manufacturers and retailers to establish a consistent fit in brassieres. Popular retailers provide customers with professional bra fitters, and bra-fitting checklists have been developed according to professional recommendations (McGhee & Steele, 2010). Despite these efforts, an accurate bra fit often remains elusive; more than 80% of women regularly wear an incorrect bra size (McGhee & Steele, 2010; Wood, Cameron, & Fitzgerald, 2008). The major reason might be the fact that every female has different breast shapes and anatomical structures around the breasts.

As a close-fitting garment worn right next to the skin, a brassiere raises important issues related to comfort, specifically pressure on the body. According to Liu, Miao, Dong, and Xu (2017), the comfortable level of pressure exerted by bra under-bands ranges from 2.0 to 2.7 kPa. A similar amount of pressure was reported along the bra underwires in the range of 2.14–2.68 kPa (Wang et al., 2009). Respiration had little influence on pressure differences, but the distribution of pressure changed depending on the brassiere and wearer, even though the bra and breast sizes remained the same (Liu, Miao, Dong, & Xu, 2017). This indicates that a standard bra cannot satisfy all wearers, and, therefore, a more customized brassiere needs to be developed.

A bra underwire plays an important role in determining bra fit and performance. The flat pattern design of bra cups and bands is based on underwire shape, size, and center height (Shin, 2010). The underwire provides a solid foundation for the bra cup and helps to lift, separate, shape, and support breasts. A typical underwire is made of metal, such as steel or nickel titanium, and forms a U shape (Yip, 2016). This wire is encased in channeling at the lower half of the bra cup, where one end of the underwire is close to the center of the body, and the other end is located near the armpit. By providing local rigidness and stiffness to the bra cup, the underwire enhances support of the bottom and sides of the brassiere (Lee & Hong, 2007; Yip, 2016).

Brassieres are more comfortable when the underwire conforms closely to the breast root contour of the wearer, as well as to the thorax and body curves. Manufactured by a casting, however, conventional metal underwire had a lot of restriction in terms of the variety in wire size and shapes. Since the majority of breast weight is supported from the bottom of a bra cup near the underwire (Zheng et al., 2009), an ergonomically designed underwire is expected to provide better support for the breast by increasing the contact area between the body and the underwire (Yip, 2016).

According to Lee and Hong (2007), women have two different types of breast root shapes, symmetrical and skewed, and breasts with skewed roots have more difficulty with standard underwires. In both types of breast roots, the lateral side was more curved than the medial side. However, the conventional underwires are shaped in the opposite way; there is more curvature on the medial side and less on the lateral side. The shape discrepancy between breast roots and wires was more severe with skewed breast roots and, therefore, greater discomfort was reported by people with skewed breast roots (Lee & Hong, 2007).

A 2-D underwire is difficult to match with a 3-D breast root shape (Yip, 2016). There have been attempts to convert the 3-D contour of breast root into 2-D underwires through mathematical calculations, and a transformation matrix algorithm was designed for 28 different types of breasts (Liu, Istook, Liu, & Wang, 2018). Another approach involved molding a 2-D underwire into a 3-D shape (Cheng, 2011; Cheung, 2014). In the proposed design of the standard 3-D wire, the upper edge of the underwires protruded from the breast root. To conform to the ribcage, the medial and lateral end points were designed to curve posteriorly inward at 30° to 85°. These 3-D underwires were reported to have a higher bust point and a shorter bust span, which indicated better breast support (Cheung, 2014).

In terms of underwire length, there has not been any regulated system proposed for either the industry or academia. Cha (2012) classified the breast shapes of Chinese women into four different types: flat, dome, protruding, and cone shapes, but the length of the breast roots was not significantly different among the breast types and ranged between 200 mm and 210 mm. Commercial underwire lengths are reported to range between 210 mm and 222 mm for size 34B and between 223 mm and 240 mm for size 36B (McCunn, 2008). This was considerably different from the dimension claimed by another report (Bra Builder, 2019), in which underwires were 206 mm and 222 mm long for sizes 34B and 36B, respectively. Therefore, the decision about where to locate the innermost and outermost points of the bra cup has been left to the bra designer’s discretion to choose underwire styles.

In our research, we took a new approach to improving bra performance. Although many prior investigators pointed out problems associated with bra fit and performance, as well as underwire, there has not been any specific insight or technical solution to address these issues. A bra underwire was selected as a key component in bra design in this research. Since no evidence was found in the literature suggesting how a bra underwire needs to be developed, we focused on whether a brassiere performs better in terms of support and comfort after adjusting underwire shape and length.

Research Method

This experimental research was designed to investigate whether bra performance could be improved with customized underwires in 3-D shapes. We investigated the two research questions as follows:

Compared to conventional 2-D underwires, do customized 3-D printed underwires significantly improve bra performance in terms of comfort and support?

In terms of comfort and support, is bra performance affected by the length of the customized 3-D printed underwires?

Experimental Underwire

Two conventional underwires were supplied by Sew Sassy Fabrics, LLC (Huntsville, AL) in sizes 34B and 34C. Both were flat steel wires with polymer-covered tips on each end, where different colors indicated the size. The medial end points of the conventional underwire were supposed to be located at the bust point level (Fairbanks, 2016), and the lateral points were 25.4 mm above the bust point (Figure 1A). Compared to size 34B, the 34C wire covered more of the medial and lateral sides (Figure 1A). Both underwires were 1 mm thick and 3 mm wide, and the length was 225 mm and 235 mm for 34B and 34C, respectively.

Figure 1.

Conventional underwires (A) and measurement points (B).

The first step to customize the underwire was to acquire the breast root contour using a body scanner (Size Stream, LLC, Cary, NC), a full body measurement system that creates a 3-D body contour and enables detailed measurement of a subject’s body. Since there was a concern that the breasts would cover the breast root, especially with large breasts, the breast was lifted slightly to reveal the breast root. A self-adhesive tape was attached around the lower part of the breast, and each tape end was anchored at the upper chest (Lee & Hong, 2007). The scanner could thus capture the breast root shape correctly while the breast remained lifted.

The scan files were processed in Geomagic Design X (3D Systems, Inc., Rock Hill, SC) to establish 3-D underwire models. Since the right-side breast is known to be harder than the left side (Loughry et al., 1987), only the right-side breast was studied for easy handling. A 3-D line was drafted on the body surface along the breast root (Figure 2A). The medial and lateral end points were located according to the conventional underwire; the medial point was kept at the bust point level, and the lateral point was placed 25.4 mm higher than the bust point (Chang & Yin, 2007). After defining the underwire contour, the width and thickness were added to this 3-D line accordingly.

Figure 2.

3-D modeling interface (A) and resulting 3-D printed underwire (B).

The underwire models were 3-D printed with a thermoplastic resin (Figure 2B) on a commercial 3-D printer, the Stratasys UPrint SE Plus (Stratasys Ltd., Eden Prairie, MN). Acrylonitrile butadiene styrene resin was selected for its relatively high flexibility and dimensional stability (Stratasys Ltd., 2017). Printing density was an important parameter that influenced the flexibility and stability of the printed wires. A 100% solid structure was chosen so that the 3-D printed underwires could be dimensionally stable while being thin. However, the bending rigidity of a 1-mm-thick resin underwire was not as high as a metal wire; it deformed easily and eventually did not return to its original shape after a certain magnitude of deformations was applied. The thickness of the customized wire had to be increased from 1 mm to 2 mm to have a comparable bending rigidity to the conventional wire.

Experimental Design

Two experiments were designed based on the two research questions. The first experiment compared bra performance between conventional and customized 3-D printed underwires. To be comparable to the conventional underwires, the 3-D printed underwire was created to have the same medial and lateral end positions as the conventional underwire. The conventional underwire was a flat 2-D wire in a standard shape (Figure 1A), while the customized underwires were 3-D in shape (Figure 2B). The 3-D printed underwires conformed to the unique breast root of each individual and were 3 mm wide and 2 mm thick.

The second experiment focused on the performance comparison among three customized 3-D printed underwires in different lengths. The medium-length underwires had medial and lateral positions identical to the conventional underwire. The longer and shorter underwires were fabricated after moving the lateral end by 25.4 mm up and down, respectively (Figure 1B). For all lengths, the medial end points were kept at the same position at the bust level. The cross-sectional dimensions of these three wires were 3 mm wide × 3 mm thick in this experiment.

Experimental Bra

Performance of the experimental underwires was evaluated through wear trials. To implement the wear trials with controlled bra size and fit, the experimental bras were created, and wear trials were administered under the following conditions:

The experimental bra provided only basic functions such as support and comfort; other auxiliary effects were not considered, such as pushing up or minimizing the breasts.

Hook and eye closures on the backband were replaced by a side-release plastic buckle. This enabled gradual adjustments of the band circumference. Subjects were allowed to adjust the bra band according to their preferred settings as well as shoulder straps.

The gore was replaced by two strings of adjustable length. Two eyes were attached to each bra cup at the inner top and bottom points (Figure 3). The length of each string was decided after measuring the distance between two breasts from each participant’s body scan. This enabled the researcher to change the distance between the two bra cups in the experimental bras so that the underwires could be located exactly on the breast root as intended.

Open-ended channeling was positioned along the bottom of the bra cup, which allowed the underwires to be replaced (Figure 3). Each participant was able to wear the same experimental bra with different underwires throughout the trials.

Figure 3.

Bra cup connection and open channeling.

According to the above conditions, the researcher created two experimental bras in sizes 34B and 34C. The bra cups for those bras were designed following the existing flat patternmaking method (Fairbanks, 2016) and composed of two panels assembled with cover stitches. The bra cups and bands were made from a cotton interlock knit (McMurray Fabrics, Inc., Aberdeen, NC), which had a 50% stretch ratio crosswise and a 65% stretch ratio lengthwise. The cups and bands were connected over the shoulder with 17-mm-wide commercial bra straps.

Research Subjects

After receiving institutional review board approval, 20 female subjects were recruited and participated in experimental sessions. To collect data from a homogenous group, research participation was limited to young (18–25) females with bra sizes of 34B or 34C, including sister sizes such as 36A, 32C, 36B, or 32D (Bengtson, 2015). The subjects were college students with an average age of 21.4 (SD = 1.85) and selected by convenience sampling. The anthropometric data of the subjects are summarized in Table 1.

Table 1.

Research Subject Information.

	Age (years)	Height (m)	Weight (kg)	BMI (kg/m²)	Bust Girth (cm)	Underbust Girth (cm)
Average	21.4	1.65	58.08	21.41	92.11	80.16
Standard error	0.41	0.01	1.19	0.40	1.21	1.08

Note. n = 20. BMI = body mass index.

Each research subject visited a laboratory twice to participate in the study. During their first visit, the subjects were body scanned and their under-breast contours were measured from the scan files. Based on the shape of each individual’s breast root, a series of 3-D wire models was designed and produced using 3-D printing. Once the custom-made wires were ready, the subjects visited the laboratory again for the wear trials. They were asked to wear the experimental bras provided by the researcher, and the underwires were changed for each trial. The subjects with breast sizes 32C, 34B, and 36A wore the 34B experimental bra and those with breast sizes 32D, 34C, and 36B had the 34C experimental bra.

Data Collection

The wear trials were conducted in a private room inside the laboratory. The subjects wore experimental bras with the underwire in the right-side bra cup. No underwire was used in the left cup during the wear trial. The bra cup was located exactly along the breast root as intended by researchers. In order to obtain accurate and precise measurements, it was necessary to ensure that the experimental bra was worn by each subject in an identical manner. Considering that each individual had different pressure preferences, the subjects were asked to adjust the length of the shoulder straps and bands to the most comfortable setting on their own. However, for internal consistency and validity, adjustment of the experimental bra was allowed only once at the beginning of the experiment, while the underwires were switched in each trial. The sequence of underwires was randomized by the researcher, and the subjects were not notified which underwire they were wearing.

Underwire performance was evaluated in two ways: objectively by measuring the pressure exerted by the underwire and subjectively by rating wearing sensations in terms of support and comfort. The pressure exerted by the underwire was observed using the Pliance-X system (Novel, Munich, Germany), which captured dynamic pressure through capacitive sensors. As shown in Figure 1B, pressure sensors were located at four different positions along the underwire between the brassiere and breast. The inner point (IP) position was selected as a medial end point and the outer point (OP) position was at the lateral end point, which varied depending on the length of the underwire. The under-breast point (UBP) was the lowest point of the underwire where the underwire met with the under-bustline. After connecting the UBP to the lowest OP, the outer under-bust point (OUP) was determined by the contact point of the breast with the underwire (Lee & Hong, 2007). The total pressure (TOT) was calculated by adding up the pressure measurements at all four points.

The subjective wearing sensation was evaluated by asking the subjects to score the support and comfort level of each experimental underwire. Support could be felt when the bra cup pushed the breast upward or inward with a certain amount of force. The feeling of comfort would be achieved when the pressing force did not exceed the individual’s level of pressure tolerance. Considering that the breast is supported by the pressure exerted by the brassiere, which can cause an uncomfortable or oppressive feeling, both sensations are related to the pressure exerted by the brassiere and its underwire. Before rating each underwire, each participant was asked to follow a series of predetermined actions, such as lifting arms over the head, rotating the upper body, and expanding the chest. Responses were recorded on a 5-point Likert-type scale, with 1 being very low support or very uncomfortable and 5 being very high support or very comfortable. Subjective wearing sensations for four measurement points (Figure 1B) were scored separately, and the overall rating (OVA) was also collected for each underwire.

Data Analysis

Statistical models were developed to assess statistical significance. In regard to the first research question, it was hypothesized that the underwire performance would not differ significantly between the conventional and customized wires, and paired t tests were conducted for statistical analysis. For the second research question, one-way ANOVA was used to test the null hypothesis that there was no performance difference among the customized underwires with different lengths. Scheffe’s post hoc tests were followed for further analysis, together with power analysis, and a .05 significance level of confidence was adopted for hypothesis testing (Howell, 2008). SPSS Statistics 24 and GPower 3.1 software packages were used.

Results and Discussion

Comparison of the Conventional and Customized Underwires

For both the conventional and customized wires, the highest pressure was measured at the UBP. The OUP was under the second largest load, and the IP had the smallest load among the four measurement points. This tendency coincided with the pressure distribution, previously reported elsewhere (Zheng et al., 2009), where most of the breast load was supported from the bottommost point. The average pressure exerted was 3.64 kPa (SD = 3.08) for conventional wires and 2.97 kPa (SD = 2.85) for customized wires. These numbers were above the range of 2.14–2.68 kPa reported in previous research (Wang et al., 2009) but stayed within a comfortable range of pressure, 2.01–4.74 kPa, in the chest area (Yan et al., 2014).

As shown in Figure 4A, the customized underwire consistently applied less pressure than the conventional wires, except at the OP. According to paired t tests (Table 2), a significant pressure difference was found only on the IP, t(38) = 3.843, p = .001, and UBP, t(38) = 2.891, p = .009. No significant difference was found at the OUP and the OP, but the total pressure was significantly lower with the customized underwire, t(38) = 3.455, p = .003. Despite the limited sample size, the statistical power stayed above .87 for all measurement points, and therefore pressure at the IP, the UBP, and total pressure could be determined as suggesting a significant difference between the conventional and customized underwires.

Figure 4.

Comparison between conventional and customized underwires; pressure (A), support rating (B), and comfort rating (C).

Table 2.

Pressure Comparison Between Conventional and Customized Underwires.

	Conventional Underwire (2-D)			Customized Underwire (3-D)			Paired Sample Test (2-D–3-D)
Point of Measure	Mean	Standard Deviation	Standard Error of Mean	Mean	Standard Deviation	Standard Error of Mean	Mean Difference	t	Significance
IP	1.555	0.930	.208	0.815	0.835	0.187	0.740	3.843	.001*
UBP	6.845	3.225	.721	5.502	2.736	0.612	1.343	2.891	.009*
OUP	4.452	2.721	.609	3.552	2.395	0.535	0.900	1.771	.093
OP	1.723	0.938	.210	2.023	2.623	0.587	−0.300	−0.510	.616
TOT	14.575	4.459	.997	11.892	5.394	1.206	2.683	3.455	.003*

Note. IP = inner point; UBP = under-breast point; OUP = outer under-bust point; OP = outer point; TOT = total sum of pressure.

*The mean difference is significant at the .05 level.

In terms of the subjective evaluation of bra support, participants gave higher ratings to the customized wire than the conventional wire at all measurement points (Figure 4B). The conventional underwire was rated 3.65 (SD = 0.88) in overall support sensation, while the rating of the customized underwire was 4.15 (SD = 0.75). It is noteworthy that the support sensation improved despite reductions in pressure. Among the four measurement points, the most support was reported at the UBP where the highest pressure was observed, and the least support was found at the IP where the lowest pressure was observed.

According to the paired t-test results (Table 3), there was a statistically significant improvement in support at all measurement points—IP, t(38) = −2.557, p = .019; UBP, t(38) = −2.896, p = .009; OUP, t(38) = −5.101, p < .000; and OP, t(38) = −2.333, p = .031)—as well as overall support, t(38) = −3.684, p = .002). Considering the limited number of research subjects, the support at the UBP, OUP, and overall had enough statistical power to suggest a significant difference at a level above .87, but the statistical power was not strong enough to suggest a support difference at the IP and OP. Participants might have been better able to sense the support from the bottom of the bra cup where the UBP and OUP were located. The IP and OP were assumed to provide a certain extent of medial and lateral support, but the level of support was low, and therefore, the change in support was difficult to verify within the given sample size.

Table 3.

Subjective Sensation Comparison Between Conventional and Customized Underwires.

Point of Measure	Conventional Underwire (2-D)			Customized Underwire (3-D)			Paired Sample Test (2-D–3-D)
Point of Measure	Mean	Standard Deviation	Standard Error of Mean	Mean	Standard Deviation	Standard Error of Mean	Mean Difference	t	Significance
Support
IP	3.35	1.268	.284	4.00	1.124	.251	−.650	−2.557	.019*
UBP	3.85	0.933	.209	4.55	0.686	.153	−.700	−2.896	.009*
OUP	3.45	1.050	.235	4.30	0.865	.193	−.850	−5.101	.000*
OP	3.75	0.851	.190	4.10	0.852	.191	−.350	−2.333	.031*
OVA	3.65	0.875	.196	4.15	0.745	.167	−.500	−3.684	.002*
Comfort
IP	3.60	0.821	.184	4.35	0.875	.196	−.750	−3.290	.004*
UBP	3.35	0.745	.167	4.30	0.733	.164	−.950	−4.046	.001*
OUP	3.70	0.733	.164	4.40	0.681	.152	−.700	−3.199	.005*
OP	3.80	0.768	.172	4.40	0.598	.134	−.600	−3.269	.004*
OVA	3.65	0.875	.196	4.35	0.587	.131	−.700	−3.390	.003*

Note. IP = inner point; UBP = under-breast point; OUP = outer under-bust point; OP = outer point; OVA = overall rating.

*The mean difference is significant at the .05 level.

In the comfort evaluation, the customized underwires also received higher ratings at every measurement point as compared with the conventional underwires (Figure 4C). The overall comfort rating increased from 3.65 (SD = 0.88) to 4.35 (SD = 0.59). Comfort scores were lowest at the UBP, where the highest pressure and support sensation were reported. According to the paired t-test results (Table 3), there was a statistically significant improvement in comfort at all measurement points—IP, t(38) = −3.290, p = .004; UBP, t(38) = −4.046, p = .001; OUP, t(38) = −3.199, p = .005; and OP, t(38) = −3.269, p = .004)—as well as overall comfort, t(38) = −3.390, p = .003. The effect on the sensation of comfort was strong enough to observe a significant difference within the given sample size. The statistical power was above .93 at every measurement point.

Comparison Between Underwires of Different Lengths

The pressure seemed to increase as the wire became longer (Figure 5A). There was less than 1 kPa exerted at the IP and slightly more pressure was observed on the OP. Regardless of wire length, the most pressure was exerted on the UBP and OUP. There were more variations in pressure at the OP since this point was located at different positions depending on wire length.

Figure 5.

Comparison between the underwires with different lengths; pressure (A), support rating (B), and comfort rating (C).

Based on the one-way ANOVA (Table 4), it was found that only the OP, F(2, 57) = 5.497, p = .007, had a significant difference in pressure among the three underwires. The pressure on the OP gradually increased as the underwire became longer. According to the post hoc test, there was no significant difference between the short- and medium-length underwires, but long underwires exerted significantly higher pressure on the OP than the short and medium length underwires. Despite the significant increase in pressure at the OP with the long underwires, the total pressure was not significantly different among the three underwires, F(2, 57) = 1.076, p = .348. The statistical power was above .83 under the given number of participants.

Table 4.

Pressure Comparison Between the Underwires With Different Lengths.

Point of Measure	Short			Medium			Long			ANOVA
Point of Measure	Mean	Standard Deviation	Standard Error of Mean	Mean	Standard Deviation	Standard Error of Mean	Mean	Standard Deviation	Standard Error of Mean	F	Significance
IP	0.833	0.768	0.172	0.787	0.844	.189	0.820	0.806	0.180	0.018	.982
UBP	6.927	3.505	0.784	7.210	2.966	.663	7.722	3.832	0.857	0.272	.763
OUP	3.763	1.962	0.439	3.667	2.290	.512	3.843	1.830	0.409	0.038	.963
OP	1.257	0.696	0.156	1.433	0.906	.202	2.513	1.936	0.433	5.497	.007*
TOT	12.780	4.942	1.105	13.09	3.815	.853	14.89	5.813	1.300	1.076	.348

Note. IP = inner point; UBP = under-breast point; OUP = outer under-bust point; OP = outer point; TOT = total sum of pressure.

*The mean difference is significant at the .05 level.

In terms of support ratings, there was no clear trend toward gradual improvement as the underwire length changed (Figure 5B). Overall support was rated lowest in the medium length underwires, while the long underwire was reported to be the most supportive. The short underwire provided more support than the medium wires but less support than the long ones. The lowest support score for the medium length wire might suggest the need to reconsider the current length of the conventional underwire.

A statistically significant difference in support sensations was found only at the OUP, F(2, 57) = 3.528, p = .035, where no significantly different pressure was observed (Table 5). It was the OP that varied in position depending on the length of underwires, but support ratings were not significantly different at this point. This could be because the support sensation came mostly from the bottom, not from the side of the underwire. Although the OUP location did not change, the change in the OP position might have affected how well the breast was supported at the OUP, where the most support was reported with the long underwire and the least support with the medium underwire. In the post hoc test, a significant mean difference (M = –.60, SD = 0.2269) was verified at the OUP between the long underwire and the medium underwire (p = .011). However, the statistical power indicated that this effect was difficult to verify within the given sample size. A larger sample size would be required to clearly verify this effect.

Table 5.

Subjective Sensation Comparison Between the Underwires With Different Lengths.

	Short			Medium			Long			ANOVA
Point of Measure	Mean	Standard Deviation	Standard Error of Mean	Mean	Standard Deviation	Standard Error of Mean	Mean	Standard Deviation	Standard Error of Mean	F	Significance
Support
IP	3.70	1.031	.230	3.80	1.151	.257	3.65	1.136	.254	0.095	.909
UBP	4.55	0.510	.114	4.20	1.056	.236	4.60	0.502	.112	1.749	.183
OUP	4.35	0.489	.109	4.00	1.026	.229	4.60	0.502	.112	3.528	.035*
OP	4.00	0.725	.162	4.05	0.759	.169	4.10	1.020	.228	0.069	.932
OVA	4.10	0.552	.123	3.95	0.825	.184	4.35	0.745	.166	1.588	.213
Comfort
IP	4.40	0.754	.169	4.25	0.851	.190	4.05	0.945	.211	0.847	.434
UBP	4.45	0.605	.135	4.15	0.745	.167	3.95	0.759	.170	2.538	.088
OUP	4.40	0.598	.134	4.00	0.918	.205	4.05	0.759	.170	1.604	.210
OP	4.30	0.9234	.2065	4.10	0.718	.161	3.70	0.865	.193	2.647	.080
OVA	4.35	0.5871	.1313	3.95	0.686	.154	3.95	0.605	.135	2.708	.075

Note. IP = inner point; UBP = under-breast point; OUP = outer under-bust point; OP = outer point; OVA = overall rating.

*The mean difference is significant at the .05 level.

From the comfort perspective, subjective ratings seemed to decrease as the underwires became longer (Figure 5C). The short underwires received the highest comfort scores above 4.0 at every measurement point. However, according to the ANOVA results (Table 5), no significant difference was found across all measurement points. The lowest comfort score was reported with the long underwire, but this was not significantly lower than with the medium and short wires. One interesting finding is that significantly higher pressure exerted on the OP did not affect the level of comfort.

Conclusion

The goal of the current research was to investigate whether customized 3-D printed underwires could improve bra performance by increasing support while enhancing comfort. Two sets of experiments were designed to study whether customized 3-D printed underwires provided significant benefits over the conventional wires, and what was the appropriate length of the underwire to maximize support and comfort, respectively. Customized underwires were produced according to the individual breast root shapes of 20 participants and compared with conventional underwires. By varying the length of the customized underwires, the researcher also studied how the length of underwires influenced bra performance.

As demonstrated in the first experiments, the customized 3-D printed underwires perform better than conventional wires. Due to their ability to conform to the unique breast root shape of each individual, the customized underwires increased the contact area and exerted significantly less pressure overall than the conventional underwires. A significant reduction in pressure was found at the innermost and under-breast points (IP and UBP). In terms of subjective wearing sensations, the support and comfort ratings were significantly higher with the customized wires than the conventional wires. Comfort increased noticeably at every measurement point, while an improvement in support was verified only at the lower points (UBP and OUP). Despite the limited number of research subjects, we found through the empirical data that a brassiere provided more support and comfort when it contained a customized underwire.

In the second set of experiments, it was initially assumed that the short underwire would provide more comfort but less support, and the experimental results partially supported this assumption. Pressure was determined to be significantly lower at the outer points (OP) when using the short and medium underwires than with the long underwires, but there was no statistical evidence that the sensation of support and comfort changed among the underwires of different lengths. This indicated that the underwire length did not cause noticeable changes in support and comfort sensations within the range of underwire length examined in this research.

The 3-D printed underwires were found to improve bra support and comfort, but it would not be possible to instantly apply the finding to bra products due to a few limitations in research design. The experimental bras employed two unconventional methods to regulate bra cup location: a buckle fastener and adjustable strings as a gore. New ways to design fasteners and gores have to be contrived before putting custom underwires into practice. Another limitation was that the 3-D printed underwire was tested only in the right-side bra cup during the wear trial. Typically, right and left breasts are not identical and an asymmetric bra structure could have affected overall bra performance. Further research is necessary to engineer the balance between two bra cups with custom underwires. Being different from conventional wires, the 3-D printed wire material could have affected the research findings as well. As 3-D printing technology is expanded to create the ability to print metallic objects from metal particles, diverse materials should be investigated to identify the best material for custom underwires.

There are several additional concerns for commercial applications of custom wires, which were not considered within this research. First of all, cost and time required to customize wires should be investigated to assess the affordability of custom underwires. Sorting breast root shapes into only a few different types could offer an effective alternative to underwires customized for each individual. Future research with a larger sample varying in breast size must be undertaken for optimal categorization of breast root shapes. In addition, durability is an important consideration in the viability of commercial underwires.

As illustrated in this research, 3-D scanning and printing promise to advance fashion product customization. By adopting 3-D technology in this research, we have suggested a technical solution to enhance bra support and comfort; however, the technical possibility demonstrated in this research is not restricted to a specific product. Advances in product customization and the resulting performance improvement would be attainable in many other fashion products. For applications in other garment components, it is important to have soft and flexible materials that are 3-D printable. Wear- and touch-friendly materials will enable broader applications of 3-D printing to the fashion industry, which is not limited to the rigid parts of products.

Footnotes

Authors’ Note

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Minyoung Suh

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