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FKM (Fluoroelastomer / Viton®) O-rings

-20 °C to 200 °C

FKM (also known as Viton®) is a premium fluoroelastomer with excellent resistance to chemicals, high temperatures, fuels, and aggressive media. A standard in the chemical industry.

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Temperature and chemical compatibility

Temperature and chemical compatibility

Temperature range: -20 °C to +200 °C (short-term up to +230 °C).

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Typical applications: chemical industry, oil and gas, engine seals, fuel systems, aviation, semiconductors.

FKM (Fluoroelastomer / Viton®)

Each elastomer has different mechanical and chemical properties.

FKM (Fluoroelastomer / Viton®) — properties and applications

FKM (Viton®, fluoroelastomer) is a premium sealing material for high temperatures and aggressive media. FKM O-rings handle temperatures from −20 to +200 °C (briefly up to +230 °C) and are typically supplied at a hardness of 75 ShA, which makes them a reliable choice wherever ordinary rubbers already fail. The material's character is clear-cut: performance under thermal and chemical load, not the lowest price. Viton® is simply a brand name for FKM — technically it's the same family of fluoroelastomers.

Chemically, FKM has excellent resistance to mineral oils, fuels, many acids, hydrocarbons and solvents, and it copes well with ester oils too. It also excels in resistance to ozone, UV and weathering, so it handles the outdoor environment as well. Thanks to this combination of thermal and chemical resistance, FKM is the standard in the chemical industry, in engines and in fuel systems, but also in aerospace and semiconductor applications — wherever a seal has to resist heat and the medium at the same time. It also has very low gas permeability, which you'll appreciate in vacuum and gas technology. If you've ever weighed up Viton vs NBR, this is the trade-off: FKM buys you heat and chemical resistance that NBR can't reach, at a higher price.

Watch the limits, though. An FKM O-ring isn't suitable for steam and hot water, for strong bases and amines (for those, reach for FEPM/Aflas), for glycol-based brake fluids, or below −20 °C, where the standard compound stiffens. These limitations have to be respected — this is exactly where the service life of the seal is decided. For low temperatures there are special low-temperature FKM compounds, which you can ask about.

Compared with the other materials, FKM stands above both NBR and HNBR in performance, but at a higher price; below it is EPDM (cheaper, but only for water, steam and brake fluids) and above it is FFKM (almost universal chemical resistance at an order-of-magnitude higher price). If temperature or chemical resistance is decisive for your application — and you don't need the extreme that calls for FFKM — an FKM O-ring is the right, proven choice.

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O-ring material comparison

Indicative values for a quick comparison. Temperature ranges are conservative (continuous service); for a specific medium always verify compatibility or consult a technician.

MaterialTemperature rangeMineral oilWaterAcidFuelHardness (Sh A)Relative price (vs NBR)
NBR-30 – 100 °C Excellent Limited Avoid Excellent70 Sh A1.0×
HNBR-30 – 150 °C Excellent Limited Avoid Excellent75 Sh A3.0×
FKM — your selection-20 – 200 °C Excellent Limited Excellent Excellent75 Sh A5.0×
FFKM-20 – 260 °C Excellent Excellent Excellent Excellent75 Sh A50.0×
EPDM-40 – 130 °C Unsafe Excellent Excellent Unsafe70 Sh A1.2×
VMQ-60 – 200 °C Avoid Excellent Avoid Avoid70 Sh A3.5×
PU-40 – 80 °C Excellent Limited Avoid Limited90 Sh A2.0×

Frequently asked questions about FKM (Fluoroelastomer / Viton®)

Is FKM the same as Viton®?
Viton® is a brand name for a fluoroelastomer (FKM) from Chemours — FKM is the general technical name for the whole family of these materials. In other words, every Viton is an FKM, but not every FKM carries the Viton brand. For most applications what matters is the type and quality of the FKM compound, not the brand itself; if you need a specific type (for example for low temperatures or bases), get in touch.
Up to what temperature does an FKM O-ring last?
FKM (Viton®) works reliably in the −20 to +200 °C range and will briefly tolerate peaks of around +230 °C. It's precisely this high temperature resistance, combined with chemical resistance, that is its main strength. Mind the lower limit — below −20 °C standard FKM stiffens; for low temperatures there are special low-temperature compounds.
When isn't an FKM O-ring enough, and you need to reach for another material?
FKM isn't suitable for hot steam and water, for strong bases and amines (those call for FEPM/Aflas), for glycol-based brake fluids, or below −20 °C. When you have extremely aggressive chemistry and high temperature at the same time, step up to FFKM. FKM is the choice for heat and most chemicals — but not for absolutely everything.

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