PTFE envelope Gasket normally consists of a rubber filler / cushion & a PTFE envelope. The filler material always will be asbestos, non-asbestos, rubber, corrugated stainless steel etc.cushion material encased in PTFE envelope and a gasket with the excellent corrosion resistance of PTFE and the strength and resilience of core material. It can be produced in several types to meet the most demanding applications.