As of today, the shoes have now entered their third iteration. Nike has dubbed the new version, the Vaporfly Next%, implying that the gain in efficiency that any one runner gets isn’t stymied at four as with the previous version. Overall, the shoe has moderate tweaks to its design. Nike markets the racing kicks as a tool to help elite marathoners break the 2-hour marathon, a human potential barrier akin, in some ways, to the plight of the 4-minute mile of the 1950s. It does this by using an ultra-lightweight midsole with superior energy return (the boost you get from the foam springing back after each foot strike) and a carbon fiber plate, embedded in the shoe, that drives the runner forward. The newest version retains these elements, adds slightly more foam, and introduces a new outer material called the Vaporweave, which is meant to work out some of the kinks in the previous versions to help the shoe withstand the elements on race day.