Nitrile Gasket Material: How to Choose the Right NBR Grade

A gasket can seal perfectly during initial testing yet still be the wrong material for the application. Oil, fuel, hydraulic fluid, compression, heat, and outdoor exposure can alter an elastomer's dimensions and mechanical properties over time. The resulting failure may appear as swelling, softening, hardening, loss of sealing force, or permanent compression set.

Nitrile butadiene rubber (NBR) is often considered when petroleum-based oils and fuels are present. However, specifying “NBR” does not fully define the material.

Two substantially different NBR-based materials are commonly used in OEM gasketing and sealing: solid NBR rubber, often called nitrile or Buna-N, and NBR/PVC closed-cell foam, also called vinyl nitrile foam. Both materials derive useful oil resistance from nitrile rubber, but their physical structures produce very different sealing behavior.

Choosing between them requires understanding what the gasket needs to do. Solid NBR is generally better suited to thin, mechanically loaded seals that require oil or fuel resistance, while NBR/PVC closed-cell foam suits applications that require lower closure force, gap conformity, cushioning, or vibration isolation.

NBR is also used as a binder in many compressed gasket sheet materials; fibers and fillers provide much of the gasket’s structure. These materials serve a different sealing function than the solid NBR rubber and NBR/PVC foam constructions discussed here. This article focuses on the two nitrile-based elastomeric constructions commonly considered for converted gaskets and seals.

Why Oil and Fuel Exposure Changes Gasket Material Selection

A gasket material must maintain its physical shape after fluid exposure. It must retain sufficient mechanical integrity and sealing force to continue functioning. Contact with an incompatible fluid can cause an elastomer to absorb the fluid and swell. Hardness, tensile strength, and elongation can also change. In a constrained gasket joint, dimensional changes can alter the stresses acting on both the gasket and surrounding components. This is why engineers should not treat oil resistance as a binary material property.

ASTM D471 evaluates changes in rubber caused by controlled exposure to liquids. Engineers can use measurements such as volume change, hardness change, tensile-strength change, and elongation change to determine whether a specific compound is suitable for the fluid and exposure conditions of an application.

NBR is useful because its acrylonitrile-butadiene polymer chemistry provides strong resistance to many petroleum oils and fuels. However, the exact performance depends on the compound formulation, fluid chemistry, temperature, and exposure duration.

The next decision is whether that NBR needs to behave like a dense rubber seal or a compressible foam gasket [E1] ..

Solid NBR Rubber: When the Seal Needs Mechanical Strength and Fluid Resistance

Solid NBR is a dense elastomer without the cellular structure of foam. That distinction matters mechanically. A solid nitrile gasket generally requires more force to deform than a soft cellular gasket. In return, it can provide greater mechanical strength, abrasion resistance, and dimensional stability in applications where the gasket is exposed directly to oils, lubricants, or fuels.

Typical applications include equipment gaskets, flange seals, oil-resistant pads, washers, machinery components, and seals for lubricated mechanical systems. Solid NBR becomes particularly attractive when the design requires:

· Direct contact with petroleum-based oils or fuels

· A relatively thin, mechanically durable gasket

· Resistance to abrasion or physical handling

· Controlled hardness or durometer;

· Higher compressive loading than a foam gasket would normally experience

The tradeoff is conformability. If an enclosure has a large gap, an irregular flange, low closure force, or significant tolerance variation, forcing a solid rubber gasket to conform to that geometry may require more clamp load than the assembly can comfortably provide.

That's where cellular NBR-based materials become interesting.

NBR/PVC Foam: Using Nitrile in a Compressible Closed-Cell Structure

NBR/PVC foam combines nitrile butadiene rubber with polyvinyl chloride to form a cellular material. It is commonly called vinyl nitrile foam. The blend changes the material's engineering role. Rather than behaving like a dense rubber sheet, NBR/PVC foam can be manufactured with a closed-cell structure that compresses relatively easily. The cell structure allows the gasket to conform to flange variations while resisting air and moisture intrusion when compressed appropriately.

The NBR portion resists oils and fuels, while PVC can provide flame-retardant characteristics and other useful properties depending on the formulation. EMI's existing material guidance identifies vinyl nitrile foam as particularly useful where oil/fuel resistance, flame performance, and compression recovery are required.

Typical NBR/PVC foam applications include HVAC equipment, transportation assemblies, industrial enclosures, insulation, gasketing, sound management, vibration isolation, and protective padding.

Published product properties vary considerably by grade. For example, one manufacturer describes vinyl/nitrile closed-cell foam families with compression-deflection ranges of approximately 2–5, 5–9, and 9–13 psi (13.8–89.6 kPa) at 25% compression.

Those ranges illustrate why specifying only “NBR/PVC foam” is insufficient. Firmness, thickness, density, compression deflection, and compression set must still match the joint.

NBR Rubber vs. NBR/PVC Foam for Gaskets and Seals

The important distinction isn't which material has more desirable properties. It's how each material behaves in the assembly.

  
        Design Requirement
        Solid NBR Rubber
        NBR/PVC Closed-Cell Foam
      
        Oil/fuel resistance
        Often a primary strength
        Often a primary strength
      
        Closure force
        Higher
        Lower
      
        Conformability to gaps
        Limited relative to foam
        High
      
        Mechanical strength
        Higher
        Lower
      
        Abrasion resistance
        Generally higher
        Application/grade dependent
      
        Cushioning
        Limited
        Good
      
        Vibration/shock absorption
        Moderate/application dependent
        Often advantageous
      
        Flame-retardant options
        Compound dependent
        Strong options available
      
        Large tolerance accommodation
        Less forgiving
        Generally better
      
        Thin mechanical seals
        Often well suited
        Application dependent
      
        Thermal/acoustic insulation
        Limited
        Often advantageous

These are selection tendencies, not universal material specifications. Validation is required for the selected grade and application.

The distinction matters most when engineers replace one gasket construction with another solely because both are labeled nitrile.

Compression Matters as Much as Fluid Resistance

Fluid compatibility gets most of the attention in NBR selection, but long-term gasket performance can also depend on compression set.

A foam gasket works because the assembly compresses it, and the material pushes back against the mating surfaces. If the cellular structure takes excessive permanent set, the gasket loses thickness and its ability to maintain contact as the enclosure moves through thermal cycles, vibration, and dimensional variation.

This can leave a gasket chemically intact but no longer sealing. For that reason, an oil-resistant gasket can still fail if compression set reduces the sealing force needed to maintain contact across the joint.

ASTM D1056 is widely used to characterize flexible cellular materials and includes classifications and test requirements applicable to cellular rubber products. Compression deflection and compression set data are especially useful for evaluating foam gasket behavior.

For solid rubber, ASTM D395 commonly measures compression set.

Engineers should avoid comparing solid NBR and NBR/PVC foam based on fluid resistance alone. A useful gasket selection process asks two independent questions:

Will the material survive the environment?
Will it maintain the mechanical conditions necessary to keep the joint sealed?

Both must be true.

Where NBR Is Usually the Wrong Direction

NBR's oil resistance does not make it a universal gasket elastomer. Outdoor weathering is an important example. When the dominant exposure is sunlight, ozone, and weather rather than petroleum fluids, EPDM may be a more appropriate material family. EMI's existing closed-cell foam guidance identifies EPDM as having strong outdoor performance while noting its weakness with oils and fuels. Vinyl nitrile presents almost the inverse tradeoff: strong oil/fuel characteristics but weaker outdoor weathering.

Temperature can be another limiting factor. EMI's current NBR/PVC application guidance cites service temperatures around 160°F (71°C) and intermittent exposure around 200°F (93°C) for the materials discussed. Other grades may differ, so the manufacturer's data for the specific material should govern the design.

Applications that combine petroleum-fluid exposure with substantially higher temperatures may require a different elastomer family, such as HNBR, fluorocarbon, or another specialty material, depending on the fluid and operating conditions.

How to Choose NBR Gasket Material for Oil and Fuel Exposure

Rather than starting with “Do I need nitrile?”, start with the joint. First, identify the fluid. Hydraulic oil, engine oil, gasoline, diesel fuel, cleaning chemicals, and refrigerant/lubricant combinations are not interchangeable exposures. Obtain compatibility data for the actual fluid, where possible.

Next, determine the mechanical requirement. A mechanically loaded flange gasket and a soft enclosure gasket may both need oil resistance but require completely different constructions.

Then determine the available closure force and gap range. If the assembly must accommodate sheet-metal variation while maintaining relatively low closure force, NBR/PVC foam may offer advantages over solid NBR. If the seal is thin, highly loaded, or exposed to abrasion, solid NBR may be the better starting point.

Evaluate temperature and weather exposure separately. Do not allow oil resistance to overshadow requirements for heat, ozone, or UV. Finally, evaluate how the material will be manufactured and assembled.

Converting NBR into Production Gaskets

Material selection and gasket geometry are closely linked. Both solid NBR and NBR/PVC foam can be converted into custom gasket configurations. Depending on material, thickness, geometry, volume, and tolerance requirements, processes can include die-cutting, knife cutting, waterjet cutting, and other fabrication methods.

Pressure-sensitive adhesive can also be laminated to a gasket to simplify assembly placement. The PSA does not necessarily provide the functional environmental seal; in many designs, its primary job is to keep the gasket accurately positioned until the joint is compressed. That distinction matters when specifying adhesive-backed NBR.

The adhesive must be compatible with the gasket surface, mating substrate, assembly temperature, and production process. Liner design, kiss-cutting, and part presentation can also affect assembly labor and positioning consistency.

Engineered Materials can prototype NBR and NBR/PVC constructions before production tooling is finalized, allowing engineers to evaluate material thickness, compression behavior, geometry, and assembly methods together.

Validate the Material in the Actual Joint

Datasheet properties serve as screening tools. Final validation should replicate the stresses that matter in the finished assembly. Depending on the application, an NBR gasket validation plan may include ASTM D471 fluid exposure, ASTM D395 compression-set testing for solid rubber, applicable ASTM D1056 testing for cellular material, thermal aging, thermal cycling, leak testing, vibration, and exposure to actual process chemicals.

For an NBR/PVC enclosure gasket, engineers should also test the expected minimum and maximum production gaps. A gasket that seals at nominal CAD dimensions may behave differently at tolerance extremes. When flame performance is required, evaluate the actual grade and applicable standard rather than assuming all NBR/PVC foam has the same rating. EMI's current vinyl-nitrile portfolio includes grades with UL 94 classifications, but ratings vary by product.

The objective is not simply to prove that the material survives testing. It is to prove that the converted gasket maintains the required seal after the combined environmental and mechanical exposures expected in service.

Choosing Between NBR Rubber and NBR/PVC Foam

NBR is a logical material family to investigate when oils and fuels make EPDM and other common gasket elastomers problematic. But “NBR material” is only the beginning of the specification. Choose solid NBR rubber when the application places greater emphasis on mechanical strength, abrasion resistance, thin-section sealing, and direct fluid exposure.

Consider NBR/PVC closed-cell foam when oil/fuel resistance must be paired with lower closure force, gap filling, cushioning, insulation, vibration management, or flame-retardant requirements. Don't select either based on polymer name alone. Fluid chemistry, temperature, compression, weathering, gasket geometry, and manufacturing tolerances ultimately determine whether the seal remains functional.

Frequently Asked Questions

Is NBR the same as nitrile rubber?

Yes. NBR stands for nitrile butadiene rubber. “Nitrile” and Buna-N are also commonly used names for this elastomer family.

Is NBR/PVC foam the same material as solid NBR?

No. NBR/PVC, often called vinyl nitrile foam, combines nitrile rubber and PVC in a cellular structure. Solid NBR is a dense elastomer. Their oil resistance may make both candidates suitable for the same environment, but their compression behavior and mechanical properties are substantially different.

When should I use solid NBR instead of NBR/PVC foam?

Use solid NBR when mechanical strength, abrasion resistance, thin-section sealing, or higher compressive loading are important. NBR/PVC foam is generally better when the gasket must accommodate larger gaps or tolerance variations with lower closure force. Fluid compatibility, temperature, and the selected grade still require validation.

Is NBR better than EPDM for gaskets?

It depends on the exposure. NBR is generally preferred when petroleum oils and fuels are important. EPDM is typically stronger against ozone and outdoor weather exposure but is generally a poor choice for petroleum oils. The specific compound and environment require validation.

What test should engineers use for NBR oil resistance?

ASTM D471 is commonly used to measure how rubber properties change after liquid exposure. Changes in volume, hardness, tensile strength, and elongation can all provide useful compatibility information.

Can NBR/PVC foam be die-cut with PSA backing?

Yes. Many NBR/PVC foams can be laminated with pressure-sensitive adhesive and converted into die-cut or kiss-cut gaskets. The foam, adhesive, substrate, and operating environment should be evaluated as a complete construction.

Engineered Materials Can Help with Material Selection

Engineered Materials can help review the application, compare NBR constructions, prototype converted gaskets, and develop production parts that meet the actual sealing and assembly requirements. Reach out to our team today.

Matt TempelisNovember 4, 2026