Polyamid fibers are made out of macromolecules that contain amide groups. The first polyamid fiber available was the Nylon CD. It is one of the lightest fibers and is characterized by high sturdiness and scrub resistance. The features of these fibers are the resistance and the high degree of elasticity. Moreover, they are crease-free and easy to dye.
You can find more information about Polyamide (PA) in Wikipedia.