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Should I use Viton or nitrile?
Use nitrile (NBR) for most oil, fuel and hydraulic seals below about 212 °F (100 °C): it costs a fraction as much and stays flexible colder. Use FKM (Viton) when heat, aromatic fuels or aggressive chemicals rule nitrile out: it serves continuously to about 400 °F (204 °C) versus 212–250 °F (100–121 °C), at roughly 5–10× the compound cost.
FKM fluoroelastomer (Viton)
Nitrile rubber (NBR)
By the numbers
Priced on the same representative part: extruded seal, rubber, 5,000 pcs.
Tensile strengthMPa
FKM
12
NBR
14
Densityg/cm³
FKM
1.85
NBR
1.2
Max service temp°C
FKM
204
NBR
100
Elongation%
FKM
200
NBR
300
Raw material cost$/kg
FKM
55
NBR
5
Which should you pick?
Pick FKM when
- Continuous heat runs between 250 and 400 °F (121–204 °C)
- The fluid is a gasoline blend or aromatic fuel
- Seals see acids and many process chemicals
- Low fuel permeation and low compression set at heat matter
Pick NBR when
- The fluid is petroleum oil, grease or hydraulic fluid at moderate temperature
- Cold service runs down to about −30 °F (−34 °C)
- O-rings and gaskets are cost-driven
- Dynamic seals need abrasion resistance
Key differences
| FKM | NBR | |
|---|---|---|
| Low-temperature limit | Stiffens below about −15 °F (−26 °C) in standard grades | About −30 °F (−34 °C) |
| Aromatic fuels and acids | Resists | Limited |
| Incompatible with | Ketones, low-molecular-weight esters, amines, hot water and steam, glycol brake fluid | Ozone, glycol brake fluid, ketones, esters and chlorinated solvents |
| Ozone and weather | Excellent | Poor |
| Upgrade path | FFKM to about 600 °F (315 °C) | HNBR to about 300 °F (150 °C) |
| Compound cost | Roughly 5–10× nitrile | Baseline |
Questions
Is Viton better than nitrile?
For heat and chemicals, yes. For cost and cold flexibility, no. Most oil and hydraulic seals below about 212 °F (100 °C) run fine in nitrile. Use FKM when temperature, aromatic fuels or chemical exposure rule nitrile out.
Is Viton the same as FKM?
Viton is a brand of FKM fluoroelastomer; other manufacturers make FKM under their own names. Call out FKM on drawings with an ASTM D2000 line callout or AMS spec rather than a brand, unless the brand is required.
Can FKM be used with brake fluid or steam?
No. Standard FKM degrades in glycol-based brake fluid, hot water and steam. EPDM is usually the better choice for those.
Why does an FKM seal cost so much more than nitrile?
Price per kilogram is part of it. FKM is also dense, about 1.85 g/cm³ versus 1.2 for nitrile, so the same seal uses about 50% more compound by weight. Together, an FKM seal often costs many times its nitrile equivalent.
Try both on your part.
The builder prices the same geometry in every suitable process and material, with DFM for each.