Selecting between EPDM (Ethylene Propylene Diene Monomer) and NBR (Nitrile Butadiene Rubber) is one of the most common material decisions facing OEM engineers. Both are widely used elastomers — but they perform almost opposite roles. Getting this wrong results in premature seal failure, leaks, and costly production shutdowns.
EPDM: Strengths & Weaknesses
EPDM excels in outdoor weathering environments: excellent resistance to UV, ozone, steam, and dilute acids. Its polar-free backbone means it resists water absorption and maintains flexibility at low temperatures to -40°C. Weakness: catastrophic oil and fuel swell — EPDM is incompatible with petroleum-based hydraulic fluids and fuels.
NBR: Strengths & Weaknesses
NBR’s nitrile groups provide outstanding resistance to petroleum oils, hydraulic fluids, and fuels — making it the standard choice for fuel system seals, hydraulic O-rings, and oil industry components. Weakness: poor UV and ozone resistance. NBR seals used outdoors must be protected from ambient ozone or they surface-crack rapidly.
Application Decision Guide
Use EPDM when: sealing against water, steam, dilute acids, or when the component is exposed to outdoor weathering. Use NBR when: sealing against petroleum oil, hydraulic fluid, diesel, or gasoline. Use HSN/HNBR when you need both oil resistance AND elevated temperature performance (to +150°C).
Blue Diamond’s Recommendation
For mixed-fluid applications (oil + water-glycol cooling), we develop proprietary NBR/EPDM blend compounds with compatibilizer chemistry. This eliminates the need for two separate seal specifications — reducing part count and stock complexity. See our custom compound case study for validation test results.
