Shoes with roughly 20 millimeters of foam underfoot. In 2009, at the peak of the barefoot-running craze, Frenchman and adventure racer Nicolas Mermoud had an idea: What if shoes could absorb a runner’s pounding like shocks on a bike? Mermoud and business partner Jean-Luc Diard tapped a Chinese chemist, who used a proprietary compound to create a shoe with 29 millimeters of foam—three times the average—without adding weight. The Hoka One One was born. Since then fat shoes have been on a tear: every major running--footwear company now makes one, and Hoka’s 2014 sales were up 350 percent over the previous year.