Inside the Fight to Design the Perfect Sports Bra

Nike's latest sports bra is an engineering marvel. Using the Flyknit technology normally reserved for sneakers, the bra is made up of just two panels of fabric—other Nike Inc. bras can have up to 41 separate sections meshed together—and promises sturdy support on the field or in the gym. It took researchers more than 600 hours of biometric testing, recording movement on cameras and creating body maps to develop the latest weapon in a battle to win over women.

A sports bra arms race has broken out among athletic wear makers. In May, Lululemon Athletica Inc. released a new crossback design called Enlite, with built-in cups and a bonded underband, in a fabric that's more like the brand's sweat-wicking yoga pants than a traditional bra. Last year, Victoria's Secret launched stretchy athletic gear line Victoria Sport. Startups such as Knix Wear and OMsignal have entered the fray, too, providing alternatives to the dominant big brands.