Of all the plastics, PTFE (Polytetrafluoroethylene) have emerged as the most common plastic gasket material. PTFE’s outstanding properties include resistance to temperature extremes from -140ºF to 450ºF (for virgin material). PTFE is highly resistant to chemicals, solvents, caustics and acids except free fluorine and alkali metals. It has a very low surface energy and does not adhere to the flanges. PTFE gaskets can be supplied in a variety of forms; either as virgin or reprocessed material, and also with a variety of filler material. The principal advantage in adding fillers to PTFE is to inhibit cold flow or creep relaxation.