Breast sizing and development of 3D seamless bra

Abstract

In intimate apparel, sizing and fit are two most important issues. The current bra sizing system has been based on bust girth and underbust girth and was developed in 1935. However, the woman's breast is a very complex 3D geometry; the existing sizing system is inappropriate to categorize breast sizes, and thus it is difficult for women to find their correct bra size. One of the purposes of this project is to develop a new bra sizing system to fit Chinese women's breast shapes and sizes. Based on the 3D nude breast measurements of 456 Chinese women subjects aged between 20 and 39, an improved bra sizing system was developed through principal components factor analysis and K-means cluster analysis of the data. The new system uses "underbust girth" and "breast depth width ratio" as the classifying parameters, which were identified as the two most critical parameters out of 103 measurements. The new bra sizing system was compared with the existing bra system in terms of accommodation (coverage) rate, efficiency of classifying the breast shape, and fit performance for the covered individuals. The study showed that, although both deploy two classifying parameters, the new bra sizing system is more efficient. It covers 97.4% of the population, provides better fit to the accommodated individuals, while maintaining a clear structure and keeping the same number of size categories. Another objective of the project is to develop seamless knitted bras with improved fitting. Based on the understanding of the breast dimensions and shapes, seamless knitted bras were developed with proper underband tension and sufficient cup strain. The key knitting parameters, including loop density, elastic yarn tension, cover yarn tension and Nylon yarn tension were investigated using factorial experimental design. It was found that the underband tension is mainly affected by the loop density and elastic yarn tension, whereas the most important factor affecting the cup strain is the loop density. Empirical prediction equations are also established for specific experimental conditions. To hold the breast shape in a natural manner, a soft 3D supporting wire prototype was designed based on the average shape of breast root of the 49 women subjects sized 75B* in the new bra sizing system. Seamless knitting is becoming popular, but existing seamless knitted bras have many problems. Therefore, we made three new seamless bra styles. Fifteen test bra samples of these 3 styles were developed using two key knitting parameters - loop density and elastic yarn tension. To test the fitting performances of the newly developed seamless knitted bras and four commercial bras (2 cut and sewn and 2 seamless knitted bras), evaluations were made of objective pressure, subjective comfort & pressure sensation and 3D breast shape on six subjects with a bra size of 75B*. The results indicated that the 3D supporting wires could provide definite support to the breasts and improve the breast vertical-sectional profiles, especially for those seamless knitted bras which have relatively larger value of loop density. Empirical equations were established to predict two pressure points at the apex and at the side of the bottomband. The research results add to our knowledge base for the development of bra sizing systems and its application to seamless knitted bra development.