FKM Chemical Compatibility: A Practical Guide

FKM – commonly known by the brand name Viton – is the default fluoroelastomer for seals that live in oil, fuel, and aggressive fluid environments. This guide explains what FKM resists, where it fails, how temperature changes the picture, and how to read a compatibility rating so you can specify the right compound the first time.

What Is FKM (Viton)?

FKM is a family of fluorocarbon elastomers with a carbon-fluorine backbone. That C-F bond is what gives the material its outstanding resistance to hydrocarbons, mineral oils, and ozone. It is widely used for O-rings, gaskets, valve seals, and custom molded parts in automotive, chemical processing, aerospace, and oil & gas.

What FKM Resists Well

• Petroleum oils and greases – excellent across the full temperature range.
• Fuels – gasoline, diesel, kerosene, and jet fuel; also biodiesel blends with graded compounds.
• Hydrocarbon solvents – benzene, toluene, xylene.
• Ozone and weather – outstanding; FKM outperforms most elastomers outdoors.
• Many acids – hydrochloric and dilute sulfuric acid are generally well tolerated.

Where FKM Struggles

• Amines and glycols – automotive coolant and glycol-based brake fluid attack FKM; use EPDM or a dedicated compound instead.
• Ketones and esters – acetone, MEK, and some esters cause swell.
• Low-molecular alcohols – methanol and ethanol swell FKM; verify with the chart.
• Steam and hot water – limited; prolonged steam service is not recommended.
• Strong bases – caustic solutions cause progressive degradation.

FKM Temperature Range

Standard FKM serves from about -20 C to +200 C continuous, with short excursions to +230 C depending on grade. Low-temperature performance depends on the specific polymer; if your application runs cold, ask for a low-temperature grade. See our FKM temperature range guide for grade-by-grade limits.

How to Read a Compatibility Rating

We rate each medium as Recommended, Limited, or Not Recommended. “Limited” means the seal may work for short contact, low concentration, or moderate temperature, but you should validate with a sample. Download the full FKM chemical compatibility chart (PDF) for a quick reference.

Pairing FKM With the Right Size

Compatibility is only half the spec. Once the compound is set, match the hardware to a standard. Use our interactive size tools to pick the correct dash number or metric size:

• AS568 O-ring size chart – inch sizes with ID, OD, and cross-section.
• ISO 3601 O-ring size chart – the international metric standard.
• JIS B2401 O-ring size chart – Japanese industrial sizes.

FAQ

Is FKM the same as Viton?

Viton is a brand name for FKM made by Chemours. “FKM” is the ASTM D1418 / ISO 1629 generic term. They are the same family of fluoroelastomers; other suppliers sell equivalent FKM under different trade names.

Can FKM handle brake fluid?

Only silicone-based brake fluid. Glycol-based brake fluid (DOT 3/4/5.1) attacks FKM; for that service use EPDM. Always confirm the fluid chemistry before specifying.

What temperature can FKM withstand?

Typically -20 C to +200 C continuous and up to +230 C intermittent, by grade. See our temperature guide for specifics.

Get a Quote

Anlintech supplies FKM / Viton O-rings, gaskets, and custom molded parts to drawing or sample, with material certification. Send your medium, temperature, and size for a quote.

Related Resources

• FKM (Viton) O-Rings – hardness and temperature options.
• Material Specification Library – data for every compound.
• Embed Our Size Charts – free tools for your site.