Knowledge · FKM O-Rings
NBR vs FKM O-Rings: Which Material Should You Choose?
Compare NBR and FKM O-rings for oil, fuel, heat, weather, cost, and chemical exposure, with compound-specific cautions and a clear buying path.
Direct answer: NBR is a common starting point for petroleum oils, mineral greases, compressed air, and many general industrial repairs. FKM is often considered for fuels, hydrocarbons, elevated temperatures, and selected chemical services. Neither material is universally better, and the exact compound and operating conditions matter.
Use this comparison as an initial screen. Confirm the exact fluid, concentration, temperature, pressure, motion, hardness, groove, and required documentation before ordering for critical service.
NBR vs FKM comparison
| Selection factor | NBR | FKM |
|---|---|---|
| Common reasons to consider | Petroleum oils, mineral greases, compressed air, general hydraulic and maintenance applications | Many fuels, petroleum oils, hydrocarbons, elevated temperatures, selected chemical applications |
| Relative cost | Usually lower | Usually higher |
| Outdoor weather and ozone | Usually a limitation | Often better than general-purpose NBR, but compound-specific |
| Low-temperature flexibility | Can be better in selected NBR grades | Can be a limitation for general-purpose FKM; special grades differ |
| Main caution | Not suited to every fuel, solvent, ozone, or high-temperature condition | Not universally resistant to amines, some alkalis, glycol-based brake fluids, steam, or every chemical |
When NBR is a practical starting point
- General petroleum-oil and grease contact
- Many hydraulic or pneumatic maintenance jobs
- Normal-temperature machinery repair
- Applications where cost and broad size availability matter
Do not identify NBR from color alone. A black O-ring can be made from several materials, and used seals can change appearance.
When FKM is worth reviewing
- Fuel or hydrocarbon exposure
- Oil combined with elevated temperature
- Applications requiring better weather or ozone resistance than general-purpose NBR
- Selected chemical services supported by exact compound data
FKM should not be described as universally chemical-resistant. Compatibility can change with the specific FKM type, fluid mixture, concentration, temperature, pressure, and exposure time.
FKM and Viton terminology
FKM is the fluoroelastomer material-family designation. Viton is a well-known fluoroelastomer brand name. A request for “Viton” should not be treated as proof that any generic FKM compound meets an exact brand, grade, certification, or performance requirement.
Information to confirm before ordering
- Exact fluid, fuel, oil, chemical, or mixture
- Concentration and contaminants
- Minimum, continuous, and peak temperature
- Pressure, vacuum, and cycling
- Static, reciprocating, rotary, or oscillating motion
- Nominal ID and cross section, groove dimensions, and required squeeze
- Hardness and tolerance
- Required certification or product-specific documentation
Buying path
- Size, material, hardness, and application confirmed: browse small packs, NBR O-rings, or FKM O-rings.
- Fluid or temperature uncertain: review the Material Guide, Chemical Compatibility Guide, and Temperature Guide.
- Drawing, unusual size, larger quantity, or critical service: use Custom O-Ring Quote.
FAQ
Is FKM always better than NBR?
No. FKM may fit higher-temperature, fuel, and selected chemical conditions, while NBR may be more practical for many general oil, grease, hydraulic, and pneumatic applications.
Can NBR be used with fuel?
Compatibility depends on the fuel composition, temperature, exposure, and exact NBR compound. Do not approve the application from the material-family name alone.
Is every FKM O-ring the same as Viton?
No. FKM describes a material family. A brand, grade, compound, or certification must be confirmed with product-specific documentation.
Can color identify the material?
No. Color is not reliable proof of polymer type or compound.
See the Technical Information, Sources & Review Policy for the limits of general material guidance.
