On May 15, 1940, a product called nylon stockings went on sale across the United States. Four million pairs sold in the first four days. Women had been wearing stockings made from silk, which came from silkworm cocoons and was expensive and fragile. Nylon was cheaper, stronger, and could be made in a factory. Nylon was created by a chemist named Wallace Carothers at the DuPont company. Carothers was studying how small molecules link together to form long chains. In 1935, one of his team members stretched a heated chemical mixture and pulled out a long, thin fiber that was surprisingly strong. When they tested it, the fiber could be stretched like elastic but snapped back into shape. This was the birth of synthetic fabric. The word "synthetic" means made by humans rather than found in nature. Cotton comes from plants. Wool comes from sheep. Silk comes from worms. Nylon comes from a laboratory. The chemicals used to make nylon come from petroleum, which is a type of oil found underground. The process involves heating these chemicals to extreme temperatures, which causes the molecules to bond into long polymer chains. Today, nylon is used in everything from toothbrush bristles to parachutes, guitar strings, and car tires.