O-Ring Material Selection Guide: NBR, FKM, EPDM & Silicone

Choosing the right O-ring material is one of the most critical decisions in seal design. Select the wrong elastomer, and you risk premature seal failure, equipment downtime, and costly warranty claims.

With dozens of rubber compounds available, where do you start?

This guide covers the four most common O-ring materials — NBR, FKM, EPDM, and Silicone — with a practical comparison to help you specify the right one for your application.

Key Takeaways (TL;DR)

• Start with temperature and fluid. Those two constraints eliminate most candidates immediately.
• NBR — lowest cost; best for oil, fuel, and grease to 120°C; fails in ozone, weather, and steam.
• FKM / Viton — best fuel and chemical resistance to 205°C; highest cost; avoid glycol brake fluid.
• EPDM — best weather, ozone, and steam/water resistance to 150°C; incompatible with petroleum oil.
• Silicone — widest temperature range (−60 to 230°C) and the only broad food/medical grades; weak in oil and abrasion.
• Rule of thumb: default to NBR, and step up only when temperature, fluid, or compliance (FDA/ISO) forces it.

Why O-Ring Material Selection Matters

FKM/Viton O-Rings are simple components, but they perform a complex job: maintaining a reliable seal under pressure, temperature, and chemical exposure. The material determines whether the seal will:

• Resist the media it contacts (fuel, oil, water, chemicals)
• Survive the temperature of the operating environment
• Maintain compression set over the service life
• Comply with industry standards (FDA, USP, aerospace, automotive)

A material mismatch is the #1 cause of O-ring failure in the field.

The Big Four: O-Ring Materials Compared

1. NBR (Nitrile / Buna-N)

NBR (Nitrile Butadiene Rubber) is the most widely used O-ring material, chosen for its excellent oil and fuel resistance at a reasonable cost.

Property	NBR
Temperature range	-40°C to +120°C
Oil/fuel resistance	Excellent
Chemical resistance	Good against oils, fuels, greases
Weather/ozone resistance	Poor
Cost	Low
Hardness range	40–95 Shore A
Common standard	ASTM D2000 BF, BG, BK

Best for: Automotive fuel systems, hydraulic seals, oil field equipment

Not ideal for: Ozone exposure, ketones, strong acids, outdoor weathering

2. FKM (Fluorocarbon / Viton)

FKM (fluoroelastomer) is the premium choice for extreme conditions — high temperature, aggressive chemicals, and demanding industrial applications.

Property	FKM
Temperature range	-20°C to +200°C (standard), up to +230°C (special)
Oil/fuel resistance	Excellent
Chemical resistance	Excellent against oils, fuels, acids, many solvents
Weather/ozone resistance	Excellent
Cost	High
Hardness range	50–90 Shore A
Common standard	ASTM D2000 HK

Best for: Chemical processing, aerospace, semiconductor, high-temp automotive

Not ideal for: Ketones, esters, amines, low-temperature applications (below -20°C without GLT grade)

Read more: FKM vs FPM vs Viton — What’s the Difference?

3. EPDM (Ethylene Propylene Diene Monomer)

EPDM excels in weathering, steam, and phosphate ester applications — making it the go-to for outdoor and water/steam environments.

Property	EPDM
Temperature range	-50°C to +150°C
Oil/fuel resistance	Poor
Chemical resistance	Good against steam, brake fluids, alkalis
Weather/ozone resistance	Excellent
Cost	Moderate
Hardness range	40–90 Shore A
Common standard	ASTM D2000 BA, BC, BE

Best for: Automotive cooling systems, steam seals, outdoor applications, brake systems

Not ideal for: Petroleum oils, fuels, mineral oils — EPDM swells and degrades

4. Silicone (VMQ)

Silicone offers the widest temperature range of any common O-ring material and is biocompatible, making it ideal for medical and food applications.

Property	Silicone (VMQ)
Temperature range	-60°C to +230°C
Oil/fuel resistance	Poor to moderate
Chemical resistance	Moderate — good against mild chemicals, poor against oils
Weather/ozone resistance	Excellent
Cost	Moderate to high
Hardness range	25–80 Shore A
Common standard	ASTM D2000 FC, FE, GE

Best for: Medical devices, food contact, extreme low-temperature applications, electrical insulation

Not ideal for: Dynamic sealing (high friction/wear), petroleum oils, concentrated acids

Side-by-Side Comparison Table

Property	NBR	FKM	EPDM	Silicone
Max temp	+120°C	+200°C	+150°C	+230°C
Min temp	-40°C	-20°C	-50°C	-60°C
Oil resistance	★★★★★	★★★★★	★☆☆☆☆	★★☆☆☆
Fuel resistance	★★★★☆	★★★★★	★☆☆☆☆	★★☆☆☆
Chemical resistance	★★★☆☆	★★★★★	★★★☆☆	★★☆☆☆
Weather/ozone	★★☆☆☆	★★★★★	★★★★★	★★★★★
Steam resistance	★★☆☆☆	★★★☆☆	★★★★★	★★★☆☆
Compression set	★★★☆☆	★★★★☆	★★★★☆	★★☆☆☆
Cost	$	$$$$	$$	$$$

How to Select the Right O-Ring Material

Step 1: Identify Your Operating Temperature

• Below -40°C → Silicone or EPDM
• -20°C to +120°C → Any material (choose based on chemical resistance)
• +120°C to +150°C → EPDM, FKM, or Silicone
• +150°C to +200°C → FKM
• Above +200°C → FKM (special grade) or Silicone

Step 2: Check Chemical Compatibility

• Petroleum oils/fuels → NBR or FKM
• Hydraulic fluids → NBR or FKM
• Steam/hot water → EPDM
• Brake fluid (glycol-based) → EPDM
• Acids/solvents → FKM
• Food/medical → Silicone (FDA-compliant grades)

Step 3: Consider Environmental Factors

• Outdoor exposure → EPDM, FKM, or Silicone (not NBR)
• Ozone exposure → Avoid NBR
• Pressure cycling → Low compression set materials (FKM, EPDM)

Step 4: Factor in Cost and Availability

• Budget-sensitive → NBR (lowest cost)
• Performance-critical → FKM (highest performance, highest cost)
• Steam/water service → EPDM (moderate cost, excellent performance)

Industry-Specific Recommendations

Industry	Primary Material	Secondary Option
Automotive (fuel)	NBR	FKM (high-temp)
Automotive (cooling)	EPDM	Silicone
Aerospace	FKM	—
Oil & Gas	FKM	NBR (lower temp)
Food & Beverage	Silicone	EPDM
Medical	Silicone	—
Chemical Processing	FKM	—
Semiconductor	FKM	—

Common Mistakes in O-Ring Material Selection

1. Choosing by price alone — A cheaper NBR seal that fails in 3 months costs more than an FKM seal that lasts 3 years
2. Ignoring chemical compatibility — “Oil resistant” doesn’t mean resistant to ALL oils; always check the specific media
3. Overlooking temperature cycling — Repeated heating/cooling accelerates compression set
4. Assuming all FKM is the same — Different grades (A, B, F, GLT) have significantly different performance
5. Forgetting about installation — Harder durometer materials are harder to install; softer compounds seal better on rough surfaces

Real-World Example

A hydraulic power unit in a steel mill originally specified NBR rod seals in a mineral-oil circuit that stabilized near 110°C. The seals hardened and cracked after roughly six months, forcing a planned shutdown every two production cycles. Re-specifying the same geometry to FKM — rated for continuous −26 to +205°C service — extended the replacement interval to three years or more, about a 6× life improvement. The higher per-part cost was recovered several times over through avoided unplanned downtime. The lesson is the same for every O-ring spec: pay for the material the temperature and fluid actually demand, not the cheapest one that fits the groove.

Standards & Further Reading

O-ring materials and sizes referenced above follow widely used industry standards: ASTM D2000 for rubber classification by properties, ISO 1629:2013 for rubber and latices nomenclature, and SAE AS568 for the standard O-ring dash-number sizing system used across North America. For aerospace and oil & gas duty, also see SAE and NACE specifications referenced in our industry guides.

Conclusion

Selecting the right O-ring material comes down to three factors: temperature, chemical exposure, and cost. NBR is the workhorse for oil and fuel, FKM handles the extremes, EPDM is your steam and weather specialist, and Silicone covers the widest temperature range with biocompatibility.

When in doubt, start with your operating temperature and chemical environment — those two factors eliminate most material options quickly.

Need help selecting the right O-ring material? Anlintech manufactures custom O-rings in NBR, FKM, EPDM, and Silicone. Our engineering team can recommend the optimal compound for your application. Contact us for technical support.

Explore our Custom Rubber Parts for materials, specifications, and custom manufacturing options.