For too long, swimwear didn’t fit small-chested women—so Pepper did what they do best: they filled the gap (literally) and created Prow Swim, the first swimwear line made just for AA–B cups.

“Versatility is key,” says Maguire. “If a swimsuit has a matching coverup, we definitely see shoppers gravitate towards those styles too—everyone loves a head-to-toe look.” And with all ...