FEP (fluorinated ethylene propylene) is a melt-processable resin invented by DuPont in 1956 and sold under the trademark Teflon®. It is a copolymer of tetrafluoroethylene and hexafluoropropylene. This resin can be used in conventional injection molding and screw extrusion techniques.

It has similar chemical resistance to PTFE, but performs better over a wider temperature range. It is translucent, lubricious to the touch and feels heavy due to its high molecular weight. Its chemically inert and has very low binding with a very low extractables content and is not reactive to most chemicals, except molten alkali metals and elemental fluorine precursors at elevated temperatures.

Like many superheroes, this material does have a weakness. It does not sterilize well at elevated temperatures (over 400°F). Additionally, it can be easily scratched by abrasive materials and may deform under mechanical loads.

In injection molding, ptfe fep is very easy to work with and requires no additives or lubricants. It is very good at forming complex geometries and can be formed with an excellent surface finish. It is a poor heat conductor, however, and does not transmit thermal energy efficiently. This is why it is best to use a hot plate or avoid using a glass lid with your FEP-based laboratory vessels.

PFA (Perfluoroalkyl Vinyl Ether) and FEP (Fluorinated Ethylene Propylene) are the two most commonly used resins in single-screw extrusion of perfluoropolymer films. They have the highest processing temperatures of all of the fluoropolymers, requiring the use of a highly modified extruder with multiple heater zones and a crosshead die. The differences in their molecular structures give these resins distinct properties that make them the preferred choice for different applications.