The FEPM designation was originally directed at copolymers of tetrafluoroethylene (TFE) and propylene (P). TFE/P provides a unique combination of chemical, heat, and electrical resistance. Chemically, TFE/P resists both acids and bases, as well as steam, amine-based corrosion inhibitors, hydraulic fluids, alcohol, and petroleum fluids. TFE/P is also resistant to ozone and weather. TFE/P typically retains its remarkable chemical resistance even in high temperatures (short exposures up to 450° F, 232° C), and tests have shown that electrical resistance actually improves with heat exposure. Nor do physical properties suffer; tensile strength typically approaches 2,500 psi.
The first TFE/P compound to be commercially marketed was Aflas (a product of Asahi Glass). In a sense, Aflas defined the initial boundaries for base-resistant materials. Different grades of Aflas have different molecular weights. Most molded and extruded products are made from Aflas 150P, which has a molecular weight of about 130,000. In comparison, Aflas 100H has a molecular weight of 200,000 and is typically used where high pressures are to be sealed, such as in oil field applications. TFE/P compounds are also widely used in the chemical processing, automotive, and aerospace industries. TFE/P compounds are not as good as standard FKM-A compounds in terms of hydrocarbon resistance, but TFE/P surpasses FKM-A in resistance to strong bases, amines, and polar solvents.