Exploring re-entrant auxetic silicone structures to design bra pads

Auxetic materials, known for their negative Poisson's ratio and unique form-fitting deformation, are proposed in this study for designing bra pads to accommodate different bra cup sizes. The deformation elasticity behaviour of re-entrant auxetic structures with a bow-tie shape, made of silicone elastomer, is systematically analysed for size accommodation and shape conformity, and compared with traditional polyurethane foam and spacer fabric used in bra pads. The results indicate that the auxetic structures exhibit desirable mechanical properties, including superior elasticity and stable deformation under tensile loading. Additionally, these structures facilitate 3D shape conformity to breast shapes, thereby improving overall bra fit. Amongst the 4 different unit cell dimensions studied, the auxetic elastomer with a cell size of 9.14 mm is the most promising candidate, which has superior elasticity, linear expansion, and excellent shape conformity. This auxetic elastomer enables increases in area from an A to D cup thus offering the potential to realize a one-size-fits-more concept. The findings provide the grounds for future research endeavours that aim to develop support in different areas of bras and optimize the arrangement of unit cells to enhance the functional aspects of bras.