The top layer of the roofing membrane is made from thermoplastic polyolefin which provides you protection against UV rays. Furthermore the middle layer contains reinforcing scrim that is made from polyester or fiberglass to improve the strength and dimensional stability of the membrane. Then the bottom layer is made of thermoplastic polyolefin providing you with additional reinforcement https://stormproroofing.net/benefits-and-installation-process-of-tpo-roofing/