Engineers designed the shoe to save runners as much energy as possible. The sole, or bottom, is made with a special kind of foam. It’s very light, so runners use less energy lifting their feet. It also cushions each step, bouncing energy back to the runners wearing them.
The shoe has another unique feature. Hidden inside the sole is a carbon fiber plate. Carbon fiber is a strong, light material. Curved like a spoon, the plate works to spring runners forward.
Before selling the Vaporfly, Nike tested the shoe in the Locomotion Laboratory at the University of Colorado Boulder. The results showed that the new shoe outperformed other top models. The sole returned 87 percent of the energy to the wearer while he or she ran.