In 2013, Nike designers and engineers started developing the Vaporfly 4% system to give runners a never-before-seen combo of race-day speed and everyday cushion.
The original Zoom Vaporfly 4% featured Nike’s ZoomX foam, which weighed less and returned more energy than any foam compound before it. Nike's previous foams returned 60-65 percent of the energy runners put in with each step. The original ZoomX foam, on the other hand, returns approximately 85 percent. The tiny weight also meant Nike could pack a shoe full of ZoomX without weighing it down.
Designers then sandwiched a curved carbon fiber plate in the midsole to increase the shoe’s stiffness and give it a propulsive feel.
“I’ve heard over and over again from athletes that it puts them in good body position to be light on their feet with a quick (ground) contact time and be on to the next stride almost right away,” Heath says.
Together, the full-length plate and the bouncy new foam gave runners an unprecedented taste of efficiency. Lab tests, scores of major marathon victories and a marathon world record backed up Nike’s claim that the shoe made runners 4 percent more efficient—and proved that big shoes could go fast.
“Fast and racing no longer means just flat,” Heath says. “And a huge part of that has been the foam. Having a very responsive foam that returns (more) energy than some of our previous foams but that’s also very lightweight at the same time—those two things have to go together for this whole idea to work.”
But it could be better. The team went back to the lab.