FEP: Properties of the Fluoroplastic

What is FEP (fluorinated ethylene propylene)?

Fluorinated ethylene propylene, or FEP for short, is a high-performance fluoroplastic from the family of fluoropolymers. The material combines exceptional chemical resistance, broad thermal stability and excellent electrical insulation properties. This combination makes FEP the preferred material in demanding fields, from aerospace through electronics to medical technology.

Chemically, FEP is a copolymer. It is formed by the polymerization of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP). This structure gives rise to the properties that distinguish FEP: almost universal chemical inertness, a wide service temperature range and a smooth, non-stick surface. In addition, it has one special feature compared with many other fluoroplastics, namely optical clarity. FEP can be processed to be transparent, allowing the visual inspection of media in tubes and linings.

FEP was developed in the 1960s to provide materials for applications with high demands on heat resistance and chemical stability. Since then, the fluoroplastic has established itself in numerous industries and is continuously developed further for technically advanced applications.

Properties of FEP

The technical advantages of FEP can be traced back to a few core properties that determine the material selection in practice.

These properties give rise to a wide range of applications. In electronics, FEP serves as insulating material for cables and wires, especially in high-temperature environments. In the chemical industry, it is used as a lining for reaction vessels and pipelines. In the medical field, FEP is used for devices and catheters because of its purity and sterilizability. In aerospace, it protects wires and seals that are exposed to extreme conditions.

FEP and PTFE: related fluoroplastics

FEP and PTFE (polytetrafluoroethylene) both belong to the family of fluoroplastics and share the high chemical resistance as well as the non-stick surface. The decisive difference lies in the processing.

FEP is thermoplastic and therefore weldable. It melts at a temperature of about 260 to 280 °C and can be extruded, formed and applied seamlessly to other components. PTFE, by contrast, cannot be melt-processed and cannot be welded. It is sintered and is suitable above all for solid material, wrappings and coatings.

For material selection this means: FEP excels wherever a seamless encapsulation or a complete seal is required, for example in the chemical industry and in semiconductor manufacturing. PTFE remains the first choice when it comes to maximum temperature resistance, non-stick coatings or plain bearings. You can find more about this material in the article on PTFE O-rings.

Chemical resistance and temperature

Chemical resistance is one of the outstanding strengths of FEP. The fluoroplastic is inert to almost all acids, alkalis and solvents. This makes it indispensable wherever components come into contact with aggressive media, for example in chemical processing, in laboratories or in the semiconductor industry.

The usable temperature range is just as broad. FEP remains flexible and functional down to very low temperatures while also permanently withstanding high temperatures. How far you can thermally load the material depends in detail on the application and, in the case of encapsulated O-rings, on the core material.

Which media are critical for your specific application is best checked with our media resistance tool.

Processing: thermoplastic and weldable

FEP is produced by copolymerization of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) in an emulsion polymerization. The resulting granulate is then brought into the desired shape by extrusion or other melt processes.

Unlike PTFE, FEP is a true thermoplastic. It melts at about 260 to 280 °C and can be processed within this range. This melting temperature must be precisely controlled, because above around 280 °C the material begins to decompose, which degrades the properties and can release harmful gases. Professionals therefore use advanced thermal regulation systems to closely monitor the temperature during extrusion and welding.

Weldability is the decisive advantage over PTFE. It allows a seamless encapsulation of components and is the technical basis for FEP-encapsulated O-rings.

FEP as the jacket of encapsulated O-rings

At NH O-RING, we do not use FEP as a solid material but as the jacket of encapsulated O-rings. Here a closed FEP layer surrounds an elastomeric core. This combines the almost universal chemical resistance of the fluoroplastic with the restoring force and sealing effect of an elastomer.

The core material determines the mechanical properties and the usable temperature range. Two variants form the basis of our range:

Both variants are FDA-compliant. Which one is right is determined by the medium, temperature and installation situation. You can find a detailed overview of core materials, selection and limits in the article on FEP O-rings.

Frequently asked questions