NBR, HNBR or FKM: which material should you choose for pressure applications?

In the field of technical seals, material selection directly affects component service life, sealing stability and the overall reliability of the system. This is especially true in pressure applications, where the seal never operates in isolated conditions, but is exposed to a combination of factors: pressure, temperature, fluids, movement, duty cycles and environmental conditions.

Among the most widely used elastomers are NBR, HNBR and FKM. These three materials are commonly used, but they are not equivalent. Each one responds to different application requirements and must be evaluated according to the real operating context.

The correct choice is not about identifying the “best” material in absolute terms, but the one that is most consistent with the application. An oversized material can generate unnecessary costs, while an unsuitable material can cause premature wear, loss of elasticity, chemical degradation or plant downtime.

The role of the material in pressure applications

In a pressure system, the seal must maintain sealing performance even when operating conditions change over time. Pressure, temperature and fluid compatibility are decisive factors, but they are not the only ones.

A seal may initially be correct from a dimensional point of view, but lose performance over time if the material is not compatible with the fluid, if it cannot withstand operating temperatures, or if it undergoes permanent deformation due to continuous compression.

For this reason, material selection should be addressed during the design phase or during the review of the application. Simply replacing a seal with an apparently similar component may not be sufficient, especially when the application presents operational criticalities.

NBR: a balanced solution for many technical applications

NBR, or nitrile rubber, is one of the most widely used elastomers in general technical applications. It is commonly used in hydraulic systems, in applications involving mineral oils, greases and fuels, and in many contexts where a good balance between performance and cost is required.

The main advantage of NBR is its versatility. Under moderate operating conditions, with compatible fluids and non-extreme temperatures, it can provide good performance and adequate service life. It is therefore a frequent choice when the application does not involve particular chemical or thermal criticalities.

However, NBR shows limitations when temperature, chemical aggressiveness or long-term stress increase. In the presence of high heat, ozone, atmospheric agents or incompatible fluids, the material may lose elasticity, harden or degrade more quickly. In these cases, higher-performance materials should be considered.

HNBR: the evolution of NBR for more demanding conditions

HNBR, or hydrogenated nitrile rubber, can be considered an evolution of NBR. Through the hydrogenation process, the material gains greater stability against aging, oxidation and higher temperatures, while maintaining many of the characteristics that make NBR suitable for numerous technical applications.

From an application point of view, HNBR is often an intermediate choice between NBR and FKM. It is used when traditional NBR does not provide sufficient resistance, but the application does not necessarily require the chemical and thermal performance of a fluoroelastomer.

This material is particularly interesting in dynamic applications or systems subject to intensive duty cycles, where good mechanical performance, wear resistance and greater long-term stability are required. For this reason, it is used in the automotive sector, hydraulic applications and various technical pressure systems.

Compared with NBR, HNBR offers better resistance to heat, ozone and aging. Compared with FKM, it can be more balanced in terms of cost and mechanical behavior, although it does not reach the same levels of chemical and thermal resistance.

FKM: high performance for critical environments

FKM, or fluoroelastomer, is a high-performance material used when the application requires high chemical resistance, thermal stability and durability under severe operating conditions.

Compared with NBR and HNBR, FKM is suitable for contexts involving high temperatures, aggressive fluids, special fuels, high-performance oils or environments with significant chemical criticality. It is widely used in automotive, gas, petrochemical and technical applications where operational continuity is an essential requirement.

The cost of FKM is generally higher, but in many critical applications this investment is justified by the longer service life of the component and the reduced risk of failures or unplanned maintenance.

Despite its high performance, FKM must also be selected carefully. It is not automatically the best solution for every application. In some dynamic systems, or in contexts where the cost/performance ratio is decisive, HNBR or NBR may represent more balanced choices.

Technical differences between NBR, HNBR and FKM

The following table summarizes the main operational differences between the three materials. The values are indicative and may vary according to the specific compound formulation.

Parameter	NBR	HNBR	FKM
Resistance to mineral oils	Good	Excellent	Excellent
Chemical resistance	Medium	Good	Very high
Heat resistance	Medium	High	Very high
Aging resistance	Medium	High	Very high
Ozone resistance	Limited	High	High
Dynamic applications	Good	Very good	Good
Indicative cost	Lower	Intermediate	Higher

This overview helps clarify the positioning of the three materials, but it does not replace application analysis. The choice must always start from the real working conditions, not from an isolated theoretical evaluation.

Temperature, fluids and service life: the factors that guide the choice

One of the most common mistakes is choosing the material based only on the nominal pressure of the system. In reality, pressure is only one of the variables. An application may operate at relatively moderate pressures and still be critical due to temperature, aggressive fluids or very intensive duty cycles.

Temperature directly affects elasticity, aging and the material’s ability to maintain sealing performance over time. An unsuitable elastomer may harden, deform or lose elastic recovery. Likewise, fluid compatibility is decisive: oils, fuels, gases, solvents or chemical agents can alter the behavior of the seal and accelerate degradation.

Expected service life is also an important parameter. In an easily accessible application subject to frequent maintenance, a standard-performance material may be adequate. In a critical system, one that is difficult to access or where downtime costs are high, it may be more appropriate to select a material with greater long-term resistance.

Compression set and sealing stability

An often underestimated parameter is compression set, meaning the permanent deformation that an elastomer can retain after being compressed for a certain period.

In pressure applications, the seal must maintain its elastic capacity in order to continue providing sealing performance. If the material loses elasticity, contact pressure decreases and micro-leaks or progressive failures may occur.

NBR, HNBR and FKM behave differently in terms of compression set, especially when temperature and duty cycle duration are involved. Under moderate conditions, NBR may be sufficient. When temperature and stress increase, HNBR can offer greater stability. In extreme or chemically aggressive environments, FKM is often the most reliable solution.

There is no single best material

The comparison between NBR, HNBR and FKM should not be read as a ranking. Each material has its own optimal field of use.

NBR is an effective solution for many standard technical applications, especially when the operating context is controlled and the performance/cost ratio is important. HNBR is suitable when an improvement in mechanical resistance, thermal resistance and aging behavior is required, without necessarily reaching the performance level and cost of FKM. FKM is the most suitable choice when the application requires high chemical resistance, thermal stability and reliability under severe conditions.

The correct decision therefore comes from balancing required performance, operating environment, expected service life and the economic sustainability of the solution.

Tecnonext’s approach to material selection

Tecnonext supports customers in selecting the most suitable material starting from the analysis of the application. We do not evaluate only the type of seal, but the entire operating context: pressure, temperature, fluid, duty cycles, operating environment and service life requirements.

This approach makes it possible to identify solutions consistent with the real use of the component, reducing the risk of non-optimized choices. Material selection is not a secondary step, but a fundamental part of the technical process.

Thanks to its knowledge of elastomeric materials and its collaboration with qualified production partners, Tecnonext supports companies, technical departments and purchasing managers in defining reliable, controlled and long-lasting sealing solutions.

For a technical discussion, an application assessment or to schedule a technical visit, contact Tecnonext.

035 059 0010

info@tecnonext.it

Via Rudello, 11, 24067 Sarnico BG

FAQ – NBR, HNBR and FKM

When should NBR be selected for a seal used in pressure applications?

NBR is suitable when the application involves mineral oils, greases or fuels, with moderate temperatures and operating conditions that are not particularly aggressive.

When is HNBR preferable to NBR?

HNBR is recommended when greater resistance to heat, aging and dynamic stress is required compared with traditional NBR.

Is FKM always better than NBR and HNBR?

No. FKM offers superior performance in chemically and thermally critical environments, but it is not always necessary. The choice depends on the application.

Can material selection reduce plant downtime?

Yes. A material consistent with the operating conditions reduces the risk of premature wear, leaks and unplanned maintenance.