Thwack, thwack, thwack. The sound of flip-flops slapping city streets and college campuses is getting louder. Hollywood celebrities show up on the red carpet wearing them, and, increasingly, executives wear their favorite flip-flops around the office.

But a national chain that sells only flip-flops and sandals? Entrepreneurs Todd Giatrelis and Sarah Towne think it can work. Flip Flop Shops, which they founded in 2004, has been stepping up its competition with the likes of Old Navy and Wal-Mart for a piece of the estimated $1.5 billion flip-flop industry. Three years after opening their first store in Boston, the founders partnered with Darin Kraetsch and Brian Curin, both former executives at ice cream chain Coldstone Creamery, to franchise the concept. Today, 14 stores, scented with coconut oil and playing beach tunes, sell about 15 brands, ranging in price from $20 Havaianas to hand-sewn OluKai Akuas, made with Italian leather, for about $150 a pair. Another 25 stores are scheduled to open this year.

Among the most popular brands are Reef, of bottle-opener fame, and Rainbow Sandals, which has a cultlike following among college students. This, says Curin, is no mere fashion fad. "Jesus wore flip-flops," he says. "They aren't going away anytime soon."