Finding the Secret Sauce: Demystifying Carbon-Fiber Plates

FOUR YEARS AGO, Nike launched the Vaporfly 4%, enthralling us with the promise its name implied: running economy improved by 4 percent. Before the shoe's release, Eliud Kipchoge wore the Vaporfly while attempting to run a marathon in less than two hours in 2017's Breaking2 Project. He eventually succeeded two years later in the Alphafly Next%, the Vaporfly's beefed-up, controversial descendant.

- AMANDA FURRER

It takes a superhuman like Kipchoge to break what was once thought an impossible barrier, but stats show the average runner can also benefit from running in super shoes. In 2019, Strava data showed runners ran 4 to 5 percent faster in the Vaporfly or Next% compared to runners wearing an average trainer.

Trailing Nike, other brands dove in, releasing their own rendition of super shoes, adding a smidge of original flavor (e.g., Saucony's Speedroll tech; the decoupled midsole on the Puma Fast-R). But there are two common denominators these models share: a responsive midsole foam and a carbon-fiber plate.

The midsole foam is usually made from a polyether block amide thermoplastic (also known as Peba, or the Arkema-trademarked Pebax). Examples include Nike's Zoom X, Puma's Nitro Elite, and Saucony's PwrrunPB. Compared with standard foam (EVA), Peba is lighter, more compliant, and more resilient.

"Typically, foams act as a cushioning ingredient and plates act as a stiffening ingredient," said Rebekah Broe, director of product and performance footwear at Hoka, on a video call.

The plate limits flexibility, acting as a propulsion agent in the gait cycle. It works in harmony with the responsive foam sandwiching it, thus delivering even higher energy return as you run.

Elliot Heath, Nike product line manager, referred to the carbon-fiber plate as an "enabler." In constructing the Vaporfly and subsequent models, the Nike running footwear team focused on stiffness and propulsion. The placement of the plate as well as its shape-it has curves like a spoon-enhances your stride's toe-off.

The plate in Hoka's road racing models, for example, is fork-shaped and sits closer to the heel. It curves higher in the rear of the shoe and swoops down closer to the ground in the forefoot.