O-Ring Material Guide: NBR, Viton, Silicone and EPDM Compared
Chemical compatibility and temperature range comparison for common O-ring elastomers.
An O-ring is only as good as the material it is made from. A ring that suits one fluid or temperature can swell, harden or crack in another, so material choice is the most important decision after size.
NBR (nitrile)
NBR is the general-purpose choice. It resists mineral oils, fuels, greases and hydraulic fluids and is widely available and low in cost. It suits moderate temperatures and is not suited to strong weather, ozone or many polar fluids.
FKM (Viton-type fluoroelastomer)
FKM handles higher temperatures and resists many oils, fuels and chemicals. It is a common choice for hot oil, engine and chemical applications. It costs more than NBR and performs poorly in some fluids, such as hot water and steam for many grades, so check the grade against the media.
Silicone (VMQ)
Silicone remains flexible across a wide range of temperatures and is used in food, medical and electrical applications. It has low tear and abrasion strength, so it is a poor choice for moving seals in oil.
EPDM
EPDM resists water, steam, weather, ozone and many brake fluids and mild chemicals. It must not be used with mineral oils or fuels, which swell it.
How to pick
Identify the fluid, the temperature range and whether the seal is static or moving. Match these against the material's compatibility chart from the manufacturer. If the fluid is unusual or a mix, ask for advice before ordering.
- Mineral oil and fuel: NBR or FKM.
- Hot oil and chemicals: FKM.
- Water, steam, outdoor use: EPDM.
- Wide temperature or food/medical use: silicone, with the correct grade.
Size and hardness
O-rings are specified by inside diameter and cross-section, in millimetres or by standard size number. The usual hardness is 70 Shore A; harder grades are used for high pressure.
Key Takeaways
- Match material to the fluid and temperature first.
- NBR for oil, FKM for heat and chemicals, EPDM for water and steam, silicone for wide temperatures.
- Do not use EPDM in oil or NBR in strong weather conditions without checking.
This article is general guidance. For a recommendation for your own application, contact our engineering team. O-rings and seals →