Tetrafluoroethylene propylene (FEPM, TFE/P), also known as Aflas®,1, is a partially fluorinated polymer that is composed of both propylene and tetrafluoroethylene monomers which can be crosslinked using a variety of curatives such as peroxides.

Note
Aflas® is a registered trade mark of Asahi Glass Co.

Tetrafluoroethylene propylene is widely used in the chemical, automotive, aerospace, and oil industry. It provides some of the best all-around chemical resistance, very low gas permeability and is mainly used for the manufacture of seals and wire and cable insulation operating in harsh environments.

The typical service temperature of FEPM is between -10C and +230°C (+445°F). However, at high service temperatures FEPM is rather weak, so that the design must prevent any high loads.

This type of a copolymer offers a combination of high temperature and chemical resistance. Similar to other fluoroelastomers, it has excellent resistance to a broad range of chemicals including acids, bases, ozone, oxidizers, corrosion inhibitors, (hydraulic) oils, phosphate esters, alcohols and hot water/steam.

FEPM is not compatible with aromatic and chlorinated hydrocarbons, and some fairly common organic solvents such as MEK, toluene, acetic acid, and acetone.
Some other major disadvantages include high compression set, high glass transition temperature, low cold temperature performance, and poor extrusion resistance, especially at high temperatures, which makes FEPM difficult to process. Furthermore, it is rather expensive and, thus, only used when the components have to withstand harsh environments.