NBR vs FKM O-Rings: Which Material Should You Choose?

NBR and FKM are two of the most common O-ring materials for oil, fuel, machinery, and repair work.

If you only need a simple replacement, the choice can feel confusing. Both materials are widely used, but they are not the same. NBR is often the practical starting point for general oil and grease. FKM is often chosen when fuel, higher heat, or stronger chemical resistance matters more.

If you already know the size and material, you can search O-ring small packs. If the fluid, temperature, or material is unclear, check the Chemical Compatibility Guide or use Bulk Quote before ordering.

Quick answer

Choose NBR for many general oil, grease, hydraulic, and everyday repair jobs where cost and availability matter.

Choose FKM when fuel, higher temperature, or stronger chemical resistance is more important.

This is only a starting point. The right choice still depends on the fluid, temperature, pressure, size, hardness, and working conditions.

What is NBR?

NBR stands for nitrile rubber. It is one of the most common O-ring materials.

Many buyers choose NBR because it is practical, affordable, and widely available. It is often used for general oil, grease, hydraulic oil, and many maintenance jobs.

NBR is a good starting point when the application is not too hot and does not involve aggressive chemicals or strong fuel exposure.

What is FKM?

FKM is a fluoroelastomer material. Many buyers also know it by the common trade name Viton.

FKM is often chosen for fuel, oil, higher heat, and more demanding sealing conditions. It usually costs more than NBR, but it can be a better choice when the application is harder on the rubber.

If the O-ring is used around fuel, engines, higher temperature, or stronger fluids, FKM is often worth checking before choosing a cheaper material.

NBR vs FKM comparison

Question	NBR	FKM
Best starting point	General oil, grease, hydraulic, repair jobs	Fuel, higher heat, stronger chemical exposure
Cost	Usually lower	Usually higher
Fuel resistance	Limited depending on fuel and conditions	Often better for fuel-related use
Heat resistance	Good for many normal jobs	Better for higher temperature conditions
Good for small repairs	Yes, when conditions are simple	Yes, when fuel or heat is involved

When NBR is usually the better starting point

NBR is often a good choice when the job is simple and the working conditions are not extreme.

Common examples include:

• General oil and grease contact
• Many hydraulic oil applications
• Basic machinery repair
• Shop tools and maintenance parts
• Lower-cost replacement jobs

If the old O-ring was black and used in a general oil or grease application, NBR may be the first material to check. But color alone does not confirm material, so do not rely on color as proof.

When FKM is usually the better choice

FKM is often considered when the application is harder on the O-ring.

Common examples include:

• Fuel systems
• Engine-related sealing
• Higher temperature equipment
• Oil plus heat exposure
• More demanding industrial fluids

If the O-ring is exposed to fuel, strong heat, or unknown fluids, FKM may be safer than NBR. For unclear fluids, check compatibility before buying.

For fuel, oil, and hydraulic systems, see our guide to O-ring materials for fuel, oil, and hydraulic use.

Do not choose by material name only

Material is important, but it is not the only detail.

Before ordering, check:

• Inner diameter
• Cross section
• Hardness
• Temperature
• Fluid or chemical exposure
• Quantity needed

If you are not sure about size, start with how to measure an O-ring. If you know the size but need help matching it to a listed size, read the O-Ring Size Chart Guide.

What about Viton?

Viton is a well-known trade name often used when people talk about FKM O-rings.

In many buying situations, customers search for Viton when they are looking for FKM-type performance. On OxxRing, we use FKM as the material name because it describes the material family more clearly.

If a drawing, manual, or old supplier calls for Viton, FKM is usually the material category to review. For critical applications, confirm the exact requirement before ordering.

If FKM may not be enough for a demanding chemical or high-temperature application, read when to use FFKM O-rings instead of FKM.

Small packs or Bulk Quote?

Use Shop Small Packs when you know the size, material, hardness, and quantity you need.

Use Bulk Quote when:

• You need 100+ pcs.
• The size is not listed.
• The material is unclear.
• The O-ring is used with fuel, chemicals, high heat, or pressure.
• You have a drawing, sample, or special requirement.

If the application is fuel, oil, heat, or chemical related, it is better to ask than to guess.

Simple decision path

General oil or grease, normal temperature, simple repair:
Start by checking NBR.

Fuel, engine area, higher heat, or stronger fluids:
Check FKM first.

Unknown fluid or chemical exposure:
Use the Chemical Compatibility Guide or Bulk Quote.

Unknown size:
Measure the O-ring first before choosing material.

Final checklist before ordering

• Confirm the size is ID × CS.
• Confirm material: NBR or FKM.
• Check hardness if the application requires it.
• Check fluid and temperature exposure.
• Use Bulk Quote if the job is unclear or high-risk.

For a broader material overview, read the O-Ring Material Guide. For application examples, see Common O-Ring Applications.

FAQ

Is NBR the same as FKM?

No. NBR and FKM are different rubber materials. NBR is often used for general oil and grease. FKM is often used for fuel, higher heat, and more demanding conditions.

Is FKM better than NBR?

Not always. FKM is usually better for fuel and higher heat, but NBR is often more practical and cost-effective for many general repair jobs.

Is Viton the same as FKM?

Viton is a common trade name associated with FKM-type fluoroelastomer materials. If a buyer searches for Viton O-rings, they are often looking for FKM performance.

Can I use NBR for fuel?

It depends on the fuel and working conditions. For fuel-related applications, FKM is often worth checking, and Chemical Compatibility should be reviewed before ordering.

Should I order small packs or request a quote?

Order small packs when the size, material, and quantity are clear. Use Bulk Quote for 100+ pcs, special materials, unclear fluids, high heat, drawings, or custom requirements.