Leather. Mesh. Plastic. Synthetic. These were the four options manufacturers had to make shoes three years ago. They worked well. There are tons of leathers, ranging from pigskin to python. Synthetic composites allowed companies to lower the prices of shoes and make certain styles more breathable and flexible. But they were all variations on a similar theme. Then, in 2012, the world received a fifth option when something new burst onto the scene: Nike’s Flyknit technology.

Flyknit is yarn that enormous knitting machines—created specifically to make the shoes, and run by computers with immense processing power—weave, translating complex textural designs into single-piece uppers. According to the company press release, Nike programmers, engineers, and designers “embarked on a four-year mission of micro-engineering static properties into pliable materials” to develop the technology. They worked alongside marathoners in order to fulfill the specific needs of long-distance runners, and ultimately produced the first two Flyknit silhouettes: the Racer and the Trainer. The single-piece constructions meant that Nike had to distill all its running tech into one-time creations. It was an engineering marvel.