NBR material — a guide for O-ring seals
NBR (acrylonitrile-butadiene rubber) is the most common O-ring material for contact with mineral oils and fuels. Properties, temperatures, applications.
- Published:
- Author:
- Ing. Filip Meheš
- Category:
- Materials
- Material:
- NBR (nitrile)
NBR, also known as Buna-N or nitrile, is a synthetic rubber produced by copolymerizing acrylonitrile and butadiene. The acrylonitrile content (typically 18 to 50 %) directly governs the material's behaviour — higher ACN delivers better oil resistance but poorer low-temperature flexibility. Around 33 % ACN is the standard balanced choice for general O-rings.
Key NBR properties
NBR offers excellent resistance to mineral oils, petroleum-based hydraulic fluids, fuels (gasoline, diesel) and greases. Working temperature range is typically -30 °C to +100 °C, with low-temp grades reaching -40 °C. Standard hardness is 70 Shore A; 50, 80 and 90 Shore A grades are also available for varying pressure loads.
NBR's main weakness is poor resistance to ozone, UV radiation and weathering. For outdoor applications or long-term light exposure, EPDM or FKM is the better pick. NBR also does not handle aggressive polar solvents (acetone, ketones) or strong acids and bases.
Typical applications
NBR dominates hydraulics (both static and dynamic piston and rod seals), automotive fuel systems, pneumatic distribution (with lubricated air) and general industrial sealing. When choosing a material for a new project running mineral oil at temperatures up to 100 °C, NBR is almost always the right first call — it's inexpensive, widely available and has decades of proven performance.