How to Choose NBR: Focus on ACN Content and Mooney Viscosity

Polykem sees many buyers facing a choice between different acrylonitrile content and Mooney viscosity grades when purchasing Nitrile Rubber (NBR). These parameters are not simply grade codes — they directly affect the material's oil resistance, low-temperature flexibility and processing behavior, and issues here often don't show up on the spec sheet. They tend to surface later, during molding or once the part is already in service.

For seals, O-rings, oil-resistant hoses and gaskets, acrylonitrile content (ACN content) and Mooney viscosity are two parameters especially worth focusing on when comparing NBR grades.

Acrylonitrile Content: Oil Resistance or Low-Temperature Flexibility?

The acrylonitrile content, often shown as ACN content, is one of the main factors that determines NBR performance. Commercial NBR grades typically span an ACN range from around 18% up to 50%, and where a grade sits in that range says a lot about what it's suited for.

A higher ACN content generally provides better resistance to oils and fuels. Rubber parts made from high-ACN grades usually show less swelling after contact with these fluids. The trade-off is reduced flexibility at low temperatures — the same molecular structure that resists oil penetration also tends to stiffen up sooner in the cold.

In practice, most buyers select an ACN range based on the balance between oil resistance and temperature flexibility.

ACN Content RangeMain CharacteristicsTypical Application ConsiderationsLower ACNBetter low-temperature flexibility, but higher oil swellingSuitable for applications where cold flexibility is more important than maximum oil resistanceMedium ACNBalanced oil resistance and flexibilityCommon choice for general industrial seals, hoses and rubber partsHigher ACNBetter resistance to oils and fuels, but reduced low-temperature flexibilitySuitable for fuel hoses, oil-resistant seals and parts exposed to aggressive fluids

It's worth remembering that higher ACN content is not automatically the safer choice. For a general industrial seal working under moderate conditions, a high-ACN grade may add cost or reduce low-temperature performance without offering a practical benefit. The fluid type and minimum service temperature should be confirmed before selecting a grade, not decided by defaulting to the highest number on the datasheet.

Mooney Viscosity: How Will the Rubber Process?

Mooney viscosity gives a useful indication of how NBR may behave during mixing and forming. Typical commercial grades fall somewhere in the 40 to 90 ML(1+4) 100°C range, and this number matters just as much as ACN content once the material reaches the factory floor.

Lower-Mooney grades generally flow more easily, which can make them suitable for molded parts with fine detail. Higher-Mooney-viscosity grades behave differently — green strength is usually better, but the compound and equipment often need tighter control to get consistent results.

The right Mooney range also depends on how the rubber will actually be processed. Molded parts need enough flow to fill the mold properly without leaving voids. Extruded hoses lean the other way, needing a viscosity that holds its shape through the die rather than slumping. And if an existing NBR grade is being replaced, picking a similar Mooney viscosity usually saves time, since it limits how much the rest of the formulation needs to be re-tuned.

Mooney viscosity shouldn't be evaluated on its own, separate from ACN content. Two NBR grades can have very similar oil resistance and still behave completely differently once they're in a mixer or an extruder.

What Information Should Buyers Provide When Selecting NBR?

Before requesting a quotation or grade recommendation, it helps to have the following ready:

1. The final application, such as a seal, hose, gasket or molded part;
2. The type of oil, fuel or other fluid involved;
3. The working temperature range;
4. The preferred ACN content or current reference grade;
5. The required Mooney viscosity, packaging and order quantity.

If the exact grade isn't known yet, sharing the current material and the most important performance requirement is usually enough. That lets the supplier compare a few suitable options instead of guessing based on a product name alone.

Polykem supplies nitrile butadiene rubber grades with defined ACN content and Mooney viscosity specifications for seals, hoses, gaskets and other oil-resistant rubber applications. For parts facing higher temperatures or longer service life requirements, Hydrogenated Nitrile Rubber (HNBR) is also worth comparing against standard NBR. 

Contact our team with your application details for product specifications, packaging information and grade recommendations.