| Property | EPDM | NBR |
|---|---|---|
| Mineral oil / hydraulic fluid | Very Poor (swells badly) | Excellent |
| Petroleum fuel | Very Poor | Good |
| Water (cold and hot) | Excellent | Good |
| Steam | Excellent (to 150°C+) | Poor |
| Glycol coolant / antifreeze | Excellent | Good |
| Brake fluid (DOT 3/4 glycol-based) | Excellent — use EPDM only | NEVER — will fail |
| Ozone / weathering / UV | Excellent | Poor |
| Acids / alkalis | Good–Fair | Poor |
| Temperature range | −40°C to +150°C | −30°C to +100°C |
The single most important rule: EPDM swells in mineral oil; NBR degrades in water, steam and ozone. These two materials are not interchangeable — the fluid chemistry dictates the compound, not cost or availability. For brake fluid (DOT 3/4), specify EPDM only. For mineral hydraulic oil, specify NBR only. Confusing them is the most common O-Ring mis-specification in maintenance and causes rapid seal failure.
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