Nylon 6 and Nylon 66 are both common polyamides widely used in filaments, staple fibers, engineering plastics, and cord fabric, etc. The numbers indicate the carbon atom count in their chemical structures: Nylon 6 is made from caprolactam (6 carbons); Nylon 66 is made from adipic acid (6 carbons) and hexamethylene diamine (6 carbons).