Nike first started knitting its Flyknit uppers from thread, which uses recycled polyester as a base, but includes a range of other materials to add things like support and weather resistance. “We started with running,” says Bignell. “It was the natural place to start. All the motion goes forward when they put one foot in front of the other.” Using its knitting process, Nike created a one-piece upper that it could freely manipulate using different types of yarns. For example, the company could use weatherized thread only where the shoe actually needed it, optimizing breathability without letting in water.