FPM is a type of synthetic rubber made with fluorine, commonly used to make O-rings, seals, and gaskets that need to withstand high heat, aggressive chemicals, or petroleum-based fluids. It can handle continuous temperatures from roughly -26°C to +230°C, which is far beyond what standard rubber can tolerate. If you’ve seen the term on a spec sheet or product listing, it refers to the same family of materials also called FKM or sold under the brand name Viton.
FPM, FKM, and Viton: Same Material, Different Names
The confusion around naming is simple once you know the source. FPM is the designation used under the ISO (international) standard for rubber nomenclature. FKM is the designation used under the ASTM (American) standard. Both refer to the same category: fluorocarbon elastomers with fluorine-containing groups on the polymer chain. Viton is a brand name originally developed by DuPont in 1958 for the aerospace industry. It’s now owned by The Chemours Company and has become so dominant that many engineers use “Viton” as a generic term for all FPM/FKM rubber, similar to how people say “Band-Aid” for any adhesive bandage.
Other manufacturers produce their own versions under different trade names, including Dyneon (3M), Tecnoflon (Solvay), Dai-El (Daikin), and Fluorel. These are all fluorocarbon elastomers. The specific formulation varies between brands and grades, but they share the same fundamental chemistry.
What FPM Is Made Of
FPM belongs to the fluoroelastomer family, meaning its polymer backbone is built from carbon-to-carbon chains with fluorine atoms attached. The two primary building blocks are vinylidene fluoride (VDF) and hexafluoropropylene (HFP). The most common general-purpose grade, known as Type 1, combines just these two monomers and contains roughly 66% fluorine by weight. That high fluorine content is what gives FPM its exceptional resistance to heat and chemicals.
More specialized grades add other monomers to the mix. Some incorporate tetrafluoroethylene to boost chemical resistance. Others add perfluoromethyl vinyl ether to improve flexibility at low temperatures. The ratio of these components determines the final properties, so engineers can select a grade tailored to a specific application, whether that’s fuel system seals or chemical processing equipment.
Temperature and Mechanical Properties
FPM’s standard working temperature range spans from -26°C to +205°C or +230°C, depending on the grade. For short periods, it can handle even higher temperatures. This makes it a go-to material in environments where conventional rubbers like nitrile or EPDM would soften, crack, or decompose.
On the cold end, FPM has a notable limitation. At temperatures much below -26°C, it stiffens and loses its ability to form a reliable seal. Specialty low-temperature grades improve this somewhat, but if your application involves extreme cold, other elastomers may be a better fit.
For mechanical performance, a typical 85 Shore A hardness grade (a common midrange formulation) has a tensile strength around 9.4 MPa. Its compression set, which measures how well the material springs back after being squeezed, is about 7% after 24 hours at 100°C and roughly 13% after 24 hours at 175°C. Low compression set numbers like these mean FPM seals maintain their shape and sealing force even after prolonged exposure to heat and pressure.
Chemical Resistance: Where FPM Excels
FPM’s strongest advantage is its resistance to oils, fuels, and hydrocarbon solvents. It holds up exceptionally well against diesel fuel, mineral oil, lubricating oil, petroleum, benzene, hexane, and chlorinated solvents like carbon tetrachloride and trichloroethylene. This is why it dominates in automotive fuel systems, oil and gas equipment, and chemical processing plants where petroleum-based fluids are present.
It also resists many inorganic acids and oxidizing agents that would destroy other elastomers.
Chemicals That Damage FPM
Despite its broad chemical resistance, FPM has clear vulnerabilities. Ketones like acetone and methyl ethyl ketone will degrade it. So will esters (ethyl acetate, butyl acetate), ethers (diethyl ether, tetrahydrofuran), and organic acids like acetic acid and formic acid. Concentrated sulfuric acid, strong bases like 50% sodium hydroxide, and certain specialty chemicals such as ethylene oxide and dimethyl formamide also cause failure.
If your application involves any of these substances, FPM is not the right choice. Alternatives like FFKM (perfluoroelastomer) or PTFE-based materials offer broader chemical compatibility, though at significantly higher cost.
Common Industrial Applications
FPM has become one of the most widely used materials for O-rings and seals across multiple industries:
- Automotive: Fuel injection seals, intake manifold gaskets, and head gaskets where contact with fuel and engine oil is constant.
- Aerospace: Seals in auxiliary power units, hydraulic actuators, pumps, valves, oil reservoirs, and line fittings where both heat and aggressive fluids are present.
- Oil and gas: Seals in pumps, valves, tanks, and heat exchange equipment exposed to petroleum products at elevated temperatures.
- Semiconductor manufacturing: Seals used in wafer fabrication processes that involve corrosive chemicals and high-purity requirements.
- Chemical processing and power generation: Anywhere that demands long-term sealing against hot hydrocarbons or aggressive process fluids.
How to Choose the Right FPM Grade
Not all FPM compounds perform identically. The general-purpose Type 1 (VDF + HFP) grade works well for most fuel and oil sealing applications and offers the best overall balance of properties. If you need improved resistance to bases or better performance in automotive fluids, grades with added tetrafluoroethylene provide that. For low-temperature applications where standard FPM gets too stiff, look for grades containing perfluoromethyl vinyl ether, which stay flexible further below freezing.
Hardness is another factor. FPM compounds range from around 60 to 90 Shore A. Softer grades conform better to uneven sealing surfaces, while harder grades resist extrusion under high pressure. A 75 Shore A compound is a common starting point for general sealing, with 85 or 90 Shore A used in high-pressure systems.
When sourcing FPM parts, specifying the brand name alone (like “Viton”) isn’t enough. Each manufacturer offers multiple grades with different chemical formulations optimized for different conditions. Matching the grade to your specific temperature range, chemical exposure, and pressure requirements is what determines whether the seal lasts months or years.