2026-09-05
Choosing the wrong rubber material for an oil seal is one of the most common reasons for premature failure. The seal looks identical on the shelf, but in service the difference between NBR, FKM and EPDM is dramatic. This guide gives you a fast, practical way to pick the right one.
NBR (Nitrile, NBR) — the workhorse. -40 °C to +120 °C. Excellent with petroleum oils, mineral oils and greases. Cheap and widely available. The default choice for most engine, gearbox and hydraulic seals.
FKM (Viton®, fluoroelastomer) — the high-temperature specialist. -25 °C to +200 °C (some grades +230 °C). Excellent with synthetic oils, fuels, chemicals. 3–8× the price of NBR. Used where NBR would fail: turbocharged engines, automatic transmissions, high-temperature hydraulics.
EPDM (ethylene propylene) — the polar-fluid specialist. -50 °C to +150 °C. Excellent with water, steam, brake fluid (DOT 3/4/5.1), phosphate ester (HFD-R) hydraulic fluids. Poor with mineral oil. Used in cooling systems, brake systems and certain hydraulic circuits.
If the working temperature stays under 100 °C and the fluid is mineral oil, NBR is the obvious choice — it costs less than a third of FKM and lasts longer in this range. If the temperature routinely exceeds 130 °C, NBR will harden and crack; switch to FKM.
Many buyers default to FKM because it is “better”. For 90% of industrial seals it is over-specified and adds cost without benefit. Specify FKM only when temperature or chemical compatibility demands it.
All three materials come in 70 Shore A as standard, with 80 Shore A or 90 Shore A for higher pressure. A garter spring in the lip keeps tension. For pressures above 10 bar, pair with a PTFE or POM back-up ring.
Bottom line: Match the rubber to (a) the fluid and (b) the temperature. When in doubt, send us the operating conditions and we will recommend the right compound — NBR by default, FKM when hot or chemically aggressive, EPDM for water/steam/brake fluid.