A fluoroelastomer is a synthetic rubber in which fluorine atoms replace many of the hydrogen atoms found in conventional rubber, giving the material exceptional resistance to heat, chemicals, and fuels. The most common fluoroelastomers belong to the FKM family, defined by ASTM and ISO standards, and are widely sold under brand names like Viton, Tecnoflon, and Fluorel. If you’ve ever seen a high-performance O-ring, fuel hose, or engine gasket rated for extreme conditions, there’s a good chance it was made from fluoroelastomer.
How Fluoroelastomers Are Built
All FKM-type fluoroelastomers share one building block: vinylidene fluoride, a small molecule rich in fluorine. Manufacturers combine it with other fluorine-containing molecules to create polymer chains where fluorine atoms form a dense shield around the carbon backbone. That shield is what makes the material so chemically inert. The more fluorine packed into the chain, the better the resistance to heat and aggressive fluids.
The fluorine content typically ranges from about 62% to 69.5% by weight, depending on the type. A general-purpose fluoroelastomer (Type 1) sits around 66% fluorine and handles most applications well. A Type 2 formulation pushes fluorine content to 68–69.5%, which improves resistance to aromatic solvents and higher temperatures. Type 3 trades some chemical resistance for better flexibility in cold environments, while Types 4 and 5 add ingredients like propylene or ethylene to improve resistance to bases or reduce swelling in hydrocarbons.
Temperature and Chemical Performance
Fluoroelastomers operate continuously in a temperature window of roughly -26°C to +230°C (-15°F to +440°F), depending on the grade. Some specialty formulations can handle short excursions up to 260°C (500°F). By comparison, standard nitrile rubber (NBR), the workhorse seal material in many industries, tops out around 120°C (248°F). That gap explains why fluoroelastomers dominate in engine compartments, jet fuel systems, and chemical processing equipment.
On the chemical side, fluoroelastomers resist a wide range of substances that would destroy ordinary rubber: petroleum oils, mineral oils, common fuels, brake fluids, strong acids, silicone oils, halogenated hydrocarbons, and vegetable oils. They perform well in contact with greases, non-flammable hydraulic fluids, and many solvents. However, they are not universal. Certain chemicals cause swelling or degradation, including some amines, ketones, esters, and specific nitrogen-containing solvents. Applications involving those chemicals typically call for a perfluoroelastomer (FFKM) instead.
FKM vs. FFKM: When Standard Isn’t Enough
Perfluoroelastomers (FFKM), sold under names like Kalrez, are the premium tier. Where standard FKM resists many chemicals, FFKM offers nearly universal chemical resistance and tolerates higher temperatures. Both materials overlap comfortably in the -15°C to 205°C range, but FFKM pulls ahead above that and handles ketones, esters, and ethers that would damage standard FKM. The trade-off is cost: FFKM parts can be ten or more times the price of their FKM equivalents, so they’re reserved for the most demanding sealing applications in semiconductor manufacturing, pharmaceutical processing, and oil exploration.
FKM vs. Nitrile Rubber (NBR)
For many engineers, the real decision is whether to use FKM or nitrile rubber. FKM costs roughly five times more than NBR due to expensive raw materials and longer manufacturing times. NBR offers better flexibility at low temperatures (down to -30°C versus FKM’s -20°C) and works fine for moderate conditions. But FKM dramatically outperforms NBR in chemical resistance, heat tolerance, and long-term durability. It also holds its shape better under sustained pressure: FKM’s compression set (how much a seal permanently deforms after being squeezed) runs 10–30%, compared to 20–40% for NBR. In harsh environments, FKM’s longer service life often offsets the higher upfront price.
Where Fluoroelastomers Are Used
O-ring seals are the single largest product form. Beyond O-rings, fluoroelastomers appear in gaskets, fuel hoses, diaphragms, expansion joints, coatings, and custom-molded shapes across several industries.
In automotive applications, which account for more than half of all fluoroelastomer consumption, typical parts include shaft seals, valve stem seals, fuel injector O-rings, fuel hose liners, engine head gaskets, and turbocharger bellows. These components sit close to the engine or fuel system, where temperatures are high and chemical exposure is constant.
Aerospace uses include O-ring seals in fuel, lubrication, and hydraulic systems, along with fuel tank bladders, firewall seals, jet engine clips, and heat-sealable tubing for wire insulation. In industrial settings, fluoroelastomers serve as hydraulic seals, check valve balls, electrical connectors, flue duct expansion joints, and FDA-approved seals for food handling equipment.
How Fluoroelastomers Are Cured
Raw fluoroelastomer compound is soft and shapeable. To turn it into a durable seal or gasket, manufacturers cross-link (or “cure”) the polymer chains so they form a stable, elastic network. Two main approaches exist. One uses a chemical called bisphenol to create ionic bonds between chains, which is the standard method for general-purpose FKM. The other uses peroxides to create radical bonds, which produces parts with better chemical resistance in some environments. The choice of curing system affects the finished part’s heat tolerance, compression set, and compatibility with specific fluids, so it’s selected based on the intended application.
PFAS Regulations and Industry Impact
Fluoroelastomers fall under the broad category of per- and polyfluoroalkyl substances (PFAS), a large family of fluorine-containing chemicals facing increasing regulatory scrutiny worldwide. In 2022, 3M announced it would cease all PFAS production by the end of 2025, including its Dyneon-brand fluoroelastomers. Europe has been developing restrictions that could impose tough limits on PFAS materials.
Other major producers, including Solvay and Arkema, have taken a more targeted approach. Rather than exiting entirely, they are phasing out the most problematic processing aids, particularly fluorinated surfactants used during manufacturing. Solvay planned to phase out fluorinated surfactants by 2026, and Arkema has already transitioned most of its production to non-PFAS surfactants. The fluoroelastomer products themselves remain available from multiple manufacturers, but the regulatory landscape continues to evolve, and supply chains are shifting as a result.