Material

NBR (Nitrile / Buna-N)

NBR (Nitrile / Buna-N) is the workhorse elastomer of the sealing industry — a synthetic copolymer of butadiene and acrylonitrile, first patented in 1934. Its acrylonitrile (ACN) content, typically ranging from 14% to 50%, is tuned to trade off oil resistance against low-temperature flexibility. Higher ACN content improves resistance to petroleum oils and fuels but raises the glass transition temperature, reducing cold-weather performance. Standard, medium and high-ACN grades cover the majority of mineral-oil and fuel-sealing applications at commodity cost.

NBR O-rings — the general-purpose compound.

Material Data Sheet

Temperature range

-40°C to +120°C (low-ACN grades to -55°C)

Hardness range

40–90 Shore A

Tensile strength

10–25 MPa

Elongation

200–600%

Compression set

15–30% (70 h at 100°C)

Resists

Petroleum oils, fuels, hydraulic fluids, greases, silicone greases, water, alcohols

Avoid with

Ozone, sunlight/UV, weathering, brake fluid (glycol), ketones, esters, chlorinated solvents

Standards

AS568, ISO 3601, BS 1806, JIS B2401

Material Science

Understanding NBR composition

NBR is a synthetic copolymer of acrylonitrile and butadiene, also known under trade names such as Nipol, Krynac, and Europrene N. The ratio of acrylonitrile to butadiene determines the compound's performance characteristics:

ACN Content	Grade	Oil Resistance	Low-Temp Flexibility	Typical Use
18–22%	Low ACN	Moderate	Excellent (to -55°C)	Military, aerospace cold-weather seals
28–34%	Medium ACN	Good	Good (to -40°C)	General industrial, automotive
36–42%	High ACN	Very Good	Moderate (to -25°C)	Fuel systems, oil-immersed seals
43–50%	Very High ACN	Excellent	Limited (to -15°C)	Aggressive fuel and solvent exposure

Performance

Key advantages

Oil & Fuel Resistance

Excellent resistance to petroleum-based oils, fuels, mineral oils, and hydraulic fluids. The most economical elastomer for hydrocarbon sealing applications.

Mechanical Strength

High tensile strength, outstanding abrasion and tear resistance, good rebound resilience. Performs well in both static and dynamic sealing applications.

Low Gas Permeability

Among the lowest gas permeability of common elastomers, making it suitable for pneumatic systems and gas-handling equipment.

Cost Effectiveness

Significantly lower cost than fluoroelastomers (FKM) and perfluoroelastomers (FFKM) while covering a wide range of sealing needs. The most specified elastomer worldwide.

Compression Set

Good compression set resistance ensures reliable long-term sealing performance. Maintains seal integrity under sustained loading in groove applications.

Water Resistance

Good resistance to water, aqueous solutions, and dilute acids and alkalis. Suitable for water-based hydraulic fluids and coolant systems.

Limitations

Where NBR is not recommended

While NBR is versatile, it should not be used in the following environments:

Ozone & UV Exposure

NBR has poor resistance to ozone, sunlight, and weathering. Outdoor or ozone-rich environments cause surface cracking and degradation. Use EPDM or FKM instead.

Polar Solvents

Ketones (acetone, MEK), esters, chlorinated hydrocarbons, and nitro-hydrocarbons cause excessive swelling. Use FKM or FFKM for these media.

High Temperatures

Standard NBR grades are limited to 120°C continuous service. For temperatures above 150°C, specify FKM or HNBR compounds.

Automotive Brake Fluid

Glycol-based brake fluids (DOT 3, DOT 4) attack NBR. Use EPDM O-rings for brake system applications.

Applications

Where it's used

Hydraulic & Pneumatic Systems

Cylinder seals, piston seals, rod seals, valve seals. The default elastomer for mineral-oil hydraulic circuits operating at moderate temperatures.

Automotive & Off-Highway

Transmission seals, engine oil seals, fuel-system O-rings, V-belts, hoses, and coolant system gaskets. One of the most widely used automotive seal materials.