Nylon is a polyamide. There are two: nylon 6.6, which was invented by DuPont, and nylon 6, which was invented by BASF. DuPont had a patent on nylon 6.6 and wouldn't license it; BASF wanted to play in the polyamides market so they created a similar material using a different process. Of the two, nylon 6.6 has a higher melt point and is a little harder than nylon 6. Nylon 6.6 is a polymer of Hexamethylene diamine and Adipic acid (Hexadioic acid) both these compounds contain 6 carbon atoms each. so it is Nylon 6.6. (Which is true for nylon 6.6. Nylon 6 is polymerized caprolactam, so that's called Nylon 6 because caprolactam also has 6 carbon atoms.)