Erica Russo, the fashion director for accessories, cosmetics and intimate apparel at Bloomingdale’s, said that indeed there has been a “shift in the business.” She noted that the trend is in line with the higher-waist and roomier pants styles that have dominated fashion this season. Perhaps motivated by the same kind of contrarianism that helped elevate Birkenstocks and fanny packs, young women are embracing “granny panties” — and not just for laundry day.

“I only wear granny panties,” Julia Baylis, a willowy 22-year-old, declared proudly. Ms. Baylis and her best friend, Mayan Toledano, 27, design the boutique clothing label Me and You. Their best seller is a pair of white cotton underpants with the word “feminist” printed in pink bubble letters across the rear. Since the line’s introduction on April 7, the panties have sold out.

Besides sales, the “feminist underwear” has inspired countless Instagram “belfies” (that’s a selfie for the behind) from Me and You customers eager to show off their feminist convictions as well as their pert posteriors.

Ms. Baylis and Ms. Toledano are part of an all-female creative collective founded by Petra Collins called the Ardorous that explores feminist topics from a millennial point of view through collaborative and solo art projects. For the generation that counts both Beyoncé and Lena Dunham as feminist icons, female sexuality is wielded for one’s own pleasure.