It is made of 100% expanded PTFE, by using special process to create soft & pliabel yet very tough gasket that has excellent resistance of pressing, creep relaxation and cold flow. It can seal the uneven and damaged flanges. It possesses universal resistance against common chemicals, except melted alkali metal, fluorine at liquid and gas states. It is free from asbestos and other lung-intruding materials. it meets the FDA requirements, doesn't have any corrosion and is able to be stored without any time limits.