HNBR vs Buna-N: What's the Difference?
When you need a reliable seal in demanding environments, the choice between HNBR (Highly Saturated Nitrile) and standard Buna-N (Nitrile) o-rings comes down to chemical resistance and temperature tolerance. Both materials are oil-resistant elastomers, but HNBR offers improved performance at higher temperatures and better resistance to certain chemicals. This guide compares the two materials using a specific HNBR product as a reference point.
HNBR O-Ring Example: AS568-106
- 0.103" CS X 0.174" ID HNBR O-Rings | AS568-106 | Dash 106 | 80 Durometer (200 / Pkg.): HNBR o-rings in AS568-106, 0.174" inner diameter by 0.103" cross-section. Service range -40°F to +300°F (-40°C to +149°C). Durometer: 80 Shore A. This dash 106 size is a common small o-ring used in hydraulic and pneumatic seals. The 80 durometer provides firmness for higher-pressure applications, and the temperature range shows HNBR handles moderate heat better than standard Buna-N (typically rated to 250°F).
0.103" CS X 0.174" ID HNBR O-Rings | AS568-106 | Dash 106 | 80 Durometer (200 / Pkg.)
HNBR vs Buna-N: Key Differences
The table below summarizes the main differences between HNBR and standard Buna-N (Nitrile) o-rings based on typical published properties.
- Temperature Range: HNBR: -40°F to +300°F (as shown in the HNBR product evidence). Buna-N: typically -30°F to +250°F. HNBR offers a higher upper limit, making it suitable for hot oil or coolant systems.
- Chemical Resistance: Both resist petroleum oils, fuels, and greases. HNBR has superior resistance to high-sulfur crude oils, sour gas, and amine-based corrosion inhibitors. Buna-N performs well in standard mineral oils but degrades faster in aggressive chemical environments.
- Durometer Options: HNBR is available in 70 and 80 Shore A. The 80 durometer (as in the example product) provides a firmer seal for higher-pressure applications. Buna-N also comes in 70 and 90 durometer, but 80 is a common choice for general sealing.
- Abrasion Resistance: HNBR has better abrasion and tear resistance than Buna-N, which matters in dynamic sealing applications where the o-ring moves against a surface.
When to Choose HNBR Over Buna-N
Choose HNBR when your application involves higher temperatures (above 250°F), exposure to aggressive chemicals like sour gas or amine inhibitors, or where mechanical wear is a concern. Standard Buna-N is adequate for most hydraulic and pneumatic systems below 250°F with conventional mineral oils. For the AS568-106 size, the HNBR option is available in a 200-piece pack, which is practical for maintenance stock or small production runs.
What the Catalog Does Not Tell You
The supplied evidence confirms the HNBR product's temperature range and durometer, but does not include specific chemical compatibility charts. For a full compatibility check, consult the manufacturer's chemical resistance data. Also, while HNBR is often considered a drop-in replacement for Buna-N in the same dash size, verify that the cross-section and inner diameter match your groove dimensions. The example product uses an imperial measurement system (inches), so ensure your application uses the same units.
