Nylon 6,6, also written as nylon 6-6, nylon 66, or nylon 6/6, is a more crystalline version of nylon 6. It is also referred to as polyamide 66 or PA 66. It has improved mechanical properties due to its more ordered molecular structure. Nylon 66 for machining has improved temperature resistance and lower rates of water absorption when compared to standard nylon 6.