Nitrile (NBR) for Custom Molded Components — Properties, Applications & Specifications
Table of Contents
Nitrile rubber (NBR) resists petroleum-based oils and fuels because its acrylonitrile (ACN) content — typically 18–50% — reduces the polymer’s free volume, limiting hydrocarbon absorption and swell at the molecular level; higher ACN content increases oil resistance at the cost of low-temperature flexibility. Without this resistance, elastomeric seals absorb hydrocarbon fluids, swell beyond dimensional tolerances, lose modulus, and ultimately extrude from their groove — a failure mode common in EPDM and silicone components placed in oilfield or hydraulic environments. Fenlora molds NBR compounds from 40–90 Shore A into hydraulic piston seals, fuel system diaphragms, and shaft oil seals for hydraulic systems, automotive powertrain, and oil and gas equipment.
Material Properties & Specifications
| Common names / abbreviations | Nitrile Rubber (NBR) |
|---|---|
| Polymer structure / monomer system | Acrylonitrile and Butadiene copolymer |
| Tg (°C) / Brittle Point | -15°C to -40°C |
| Density (g/cm³) | 0.98 |
| Hardness range (Shore A/D) | 30 - 95 Shore A |
| Tensile strength (MPa) | 6.8 - 24.1 |
| Elongation at break (%) | 400 - 600 |
| 100% / 300% modulus (MPa) | 0.68 - 10.3 at 100% |
| Rebound / tanδ (temp + freq) | N/A |
| Compression set (%) | 5 - 20 % |
| Continuous service temp (°C) | -34°C to 121°C |
| Environmental & Fluid Resistance | Ozone: Poor to Fair | IRM 903: 0 to +25% |
| ASTM D2000 Callouts | M5BG714 A14 B14 EO34 Z1 |
| Electrical properties | Vol Res: 3.5 x 10^10 ohm-cm |
| Thermal properties | Thermal Cond: 0.143 - 0.24 W/mK |
| Typical formulation ranges (phr) | Treated Sulfur: 1.5 phr, TBBS: 1.2 phr |
| Tear Resistance | Tier 4 - Strong |
| Abrasion Resistance | Tier 5 - Excellent |
| Gas Impermeability Resistance | Tier 4 - Strong |
| Oxygen Resistance | Tier 2 - Limited |
| Ozone Resistance | Tier 1 - Basic |
| Weathering Resistance | Tier 2 - Limited |
| Oil Resistance | Tier 4 - Strong |
| Acid Resistance | Tier 4 - Strong |
| Alkaline Resistance | Tier 4 - Strong |
| Water Resistance | Tier 4 - Strong |
| Flame Resistance | Tier 1 - Basic |
When to Specify NBR
NBR is the default elastomer for oil-wetted dynamic and static sealing — but ACN content and compound formulation must match the fluid chemistry and temperature window precisely.
| Use NBR when… | Avoid NBR when… |
|---|---|
| Continuous contact with petroleum oils, hydraulic fluid (ISO 32–68), or diesel fuel | Exposure to ozone, UV, or weathering without protective shielding |
| Dynamic sealing applications cycling to 120°C with petroleum lubricants | Continuous service above 120°C — compression set accelerates rapidly |
| Cold-temperature flex required to −40°C (low-ACN compound, 18–26% ACN) | Phosphate ester hydraulic fluids (Skydrol) — use EPDM instead |
| Cost-sensitive applications where HNBR or FKM performance isn’t required | Strong polar solvents (ketones, esters, chlorinated hydrocarbons) — severe swell |
| Shore A 40–90 range needed with predictable compression-set behavior | Steam or hot water service — EPDM or HNBR are the correct choices |
The ACN content selection is the most consequential compound decision for NBR. A 34% ACN compound offers the best balance of oil resistance and cold flexibility for most hydraulic seals, but specifying a 45%+ ACN compound for cold-climate outdoor hydraulic equipment will cause catastrophic seal stiffening below −15°C, leading to bypass leakage at startup before the system warms. When a single compound must handle wide temperature swings and petroleum exposure, this ACN tradeoff is non-negotiable and should be defined before any tooling is cut.
Custom Parts We Make in NBR
Fenlora molds NBR into precision sealing and fluid-contact components across hydraulic, automotive, and industrial applications — each part geometry selected to exploit NBR’s dimensional stability in oil-immersed service.
→ Hydraulic piston and rod seals — NBR’s low swell in ISO VG hydraulic oils maintains the tight radial clearance these seals require; dimensional growth beyond 1–2% causes extrusion under system pressure spikes.
→ Fuel system diaphragms — Flexible NBR diaphragms in carburetors, fuel regulators, and pump bodies withstand continuous fuel immersion where silicone would swell and lose spring-rate consistency.
→ Shaft oil seals (lip seals) — NBR lip seals at 60–75 Shore A balance the radial load needed for a dynamic hydrodynamic film against shaft surface speeds up to ~6 m/s in gearboxes and axles.
→ O-rings and custom profile static gaskets — For flanged hydraulic joints, NBR remains the cost-effective standard; Fenlora compounds to AS568 or custom cross-section with controlled hardness tolerance of ±5 Shore A.
→ Grommets and cable pass-throughs in oil-prone enclosures — NBR grommets protect wiring harnesses routed through bulkheads in engine bays where petroleum mist or drip contact is unavoidable. (See Fenlora rubber grommets)
If your drawing specifies NBR or you’re working from functional requirements around fluid compatibility and hardness, contact our engineering team to discuss ACN content selection, compound formulation, and hardness range: contact us
Industries That Use NBR
Electrical
NBR grommets and conduit seals protect cable entries in control panels and junction boxes installed near machine tools, compressors, or other petroleum-wetted machinery. (Link to electrical industry) Where EPDM would be the outdoor-weathering choice, NBR is specified when the enclosure sits in a hydrocarbon-contaminated environment.
Automotive
NBR is the standard compound for crankshaft seals, transmission lip seals, and valve stem seals where continuous oil splash and sump immersion occur. The material’s resistance to engine and gear oils across the −30°C to 120°C operating window matches the thermal cycle of production vehicle drivetrains without requiring the cost premium of HNBR or FKM. (Link to automotive industry)
Industrial Machinery
Cylinder rod seals, piston seals, and accumulator bladders in mobile and stationary hydraulic systems are routinely specified in NBR 70 Shore A as a baseline compound. NBR’s predictable swell behavior in mineral-based hydraulic fluids — typically <3% volume change in ISO 46 oil at 100°C — gives design engineers a stable dimensional datum for groove design and clearance calculations.
Oil & Gas Surface Equipment
Pump stator liners, valve seats, and wellhead gaskets in surface production equipment operate in crude oil, produced water/oil emulsions, and refined hydrocarbon streams where NBR’s oil resistance prevents the progressive swelling failure that would affect EPDM or NR components. Elevated H₂S environments may require a specialty NBR compound with enhanced sour-gas resistance — this is a compound-level specification, not a material change.
Compare Materials
NBR covers most oil and fuel sealing applications, but five conditions push engineers toward alternative elastomers.
| If your application involves… | Consider instead |
|---|---|
| Outdoor UV or ozone weathering | EPDM |
| Extreme chemical or solvent resistance | Viton (FKM) |
| Continuous temps above 150°C | Silicone (VMQ) |
| High dynamic flex and tear resistance | Natural Rubber (NR) |
| High abrasion and mechanical wear | Polyurethane (AU/EU) |
| Moderate oil + weather resistance | Neoprene (CR) |
| Air/gas impermeability | Butyl (IIR) |
| Cost-sensitive general-purpose use | SBR |
Not sure which material fits your application? Send us your requirements and we’ll recommend the right compound.