Polytetrafluoroethylene and its composite gaskets are high quality sealing gaskets mainly composed of polytetrafluoroethylene. They have excellent corrosion resistance and sealing performance against chemical media, outstanding surface non-stickiness and pollution resistance, good compression resilience and creep relaxation resistance, and are especially suitable for strong corrosive media or for sanitation. Medium and low temperature seals are required in food, medicine and other industries.