O-rings play a critical role in industrial applications by preventing fluid and gas leaks. Nitrile (NBR) and fluorocarbon (FKM) are two of the most popular material choices available today. Our latest blog breaks down the key differences between NBR and FKM to assist you in selecting the ideal material for your upcoming project.
What is Nitrile?
Composed of acrylonitrile (ACN) and butadiene, NBR is a synthetic rubber whose properties depend heavily on the ACN content, which generally spans from 14% to 50%. A higher ACN concentration enhances resistance to fuels and oils, though a higher number is a factor that can worsen low-temperature performance and decrease dynamic performance. Hydrogenated NBR, or HNBR, exhibits impressive abrasion resistance and tensile strength, operating effectively across a temperature range of -40ºC to 150ºC (-40ºF to 300ºF).
What is Fluorocarbon?
FKM is a synthetic polymer renowned for its exceptional chemical stability and swell resistance when exposed to fuels and oils. Higher fluorine-based polymers can provide excellent service in oxygenated and high-octane fuel blends. It performs reliably across a temperature range of -25ºC to 230ºC (-13ºF to 446ºF) and demonstrates superior compression resistance, maintaining flexibility. Low-temperature FKM polymers can perform down to -40ºC (-40ºF).
At first glance, it might seem that NBR and FKM are too similar to discern any difference; both are synthetic, withstand cold and triple-digit temperatures, and offer useful resistance. Understanding the differences helps you choose the material best suited to your specific industrial operation.
When is Fluorocarbon Superior to Nitrile?
FKM outperforms nitrile in high-temperature applications, preserving its flexibility and sealing force up to 230ºC (446ºF)—a threshold at which NBR degrades. Additionally, NBR breaks down easily when exposed to strong mineral acids, chlorinated solvents (compounds used within industrial operations), and aromatic hydrocarbons such as benzene. FKM offers robust resistance against these aggressive chemicals, rendering it the preferred option for processing plants and other challenging industrial settings.
FKM is far better suited than nitrile for outdoor and ozone-dense applications. This advantage stems from NBR’s high vulnerability to ultraviolet degradation and ozone cracking. In scenarios requiring exposure to direct sunlight or ozone-producing electrical equipment, FKM retains its structural integrity and sealing capabilities under demanding conditions. Furthermore, FKM excels in high-pressure settings by preserving its shape and sealing effectiveness under heavy loads, whereas NBR risks deforming and causing potential leaks.
In high-wear and dynamic mechanical settings, FKM stands out due to its superior tensile strength, tear resistance, and abrasion resistance compared to HNBR. For operations involving friction, moving components, or physical wear, such as dynamic shaft seals and industrial conveyor belts, FKM resists tearing and endures physical demands much more effectively. Additionally, FKM is optimal for routine industrial applications focused on standard petroleum oil and fluid sealing, reliably handling greases, petroleum-based oils, water, and silicone fluids at temperatures under 120ºC (248ºF).
When is Nitrile Superior to Fluorocarbon?
NBR is often a highly effective option for industrial applications requiring mechanical wear resistance and flexibility in cold environments. While standard FKM offers superior heat tolerance and broader chemical resistance, it typically stiffens and loses dynamic sealing capacity around -15ºC and -20ºC (5ºF to -4ºF). In contrast, standard NBR configurations remain flexible down to -40ºC (-40ºF). Consequently, NBR is widely preferred for internal refrigeration units and protected cold-weather machinery. However, for outdoor operations, NBR’s cold flexibility must be measured against its vulnerability to ultraviolet light and ozone.
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