Silicone vs Nitrile Rubber

Silicone vs Nitrile (NBR) Rubber: Comparison Guide

Silicone rubber and nitrile rubber (NBR, Buna-N) are two of the most widely used elastomers in sealing applications. They rarely compete directly in well-specified applications because their property profiles are almost perfectly complementary — where one is strong, the other is weak. Understanding the differences guides correct material selection and avoids costly specification errors.

Chemical Resistance: The Primary Selection Factor

Nitrile's strength — petroleum oils and fuels: Nitrile rubber is the first choice for dynamic sealing against mineral oil, hydraulic fluid, petroleum fuel, and vegetable oil. Acrylonitrile content (18–50% ACN) determines oil resistance — high-ACN nitrile (50% ACN) provides excellent oil resistance but reduced low-temperature flexibility. For oil seals, O-rings in hydraulic systems, and fuel hose inner liners, nitrile is the standard material at temperatures below 100–120 °C.

Silicone's weakness — oils: Silicone rubber is poorly resistant to petroleum oils and fuels. Volume swell in IRM 903 oil at 150 °C (ASTM D471) is typically 20–60% for standard silicone — acceptable only for static seals with no dimensional criticality. For dynamic seals in oil-lubricated systems, silicone is not suitable.

Silicone's strength — temperature range: Silicone operates from −60 °C to +230 °C continuously. Nitrile begins to harden significantly below −20 °C to −30 °C (depending on ACN content and compound formulation), and embrittles and cracks below −40 °C. At the high end, standard nitrile deteriorates above 120 °C; high-temperature nitrile grades reach +150 °C maximum. Silicone is the only practical elastomeric choice for applications spanning both cold and hot extremes simultaneously.

Silicone's strength — food contact and biocompatibility: Platinum-cured silicone readily achieves FDA 21 CFR 177.2600 and LFGB §30/§31 compliance. Nitrile rubber is not generally suitable for food-contact applications — the acrylonitrile monomer (a potential carcinogen above regulatory thresholds) restricts food-contact use. Medical and pharmaceutical applications exclusively use silicone or fluoroelastomer, not nitrile.

Temperature Comparison

Mechanical Properties

At equivalent Shore hardness, nitrile rubber generally provides higher tensile strength (10–20 MPa for nitrile vs 5–12 MPa for silicone) and better abrasion resistance. For dynamic sealing applications (shaft seals, piston seals) where abrasion from sliding contact is the primary failure mode, nitrile's better abrasion resistance is an advantage. Silicone's lower tear strength and abrasion resistance make it less suitable for dynamic sliding contact applications.

Cost

Nitrile rubber compounds are typically 50–70% cheaper per kilogram than equivalent silicone compounds. For cost-sensitive sealing applications operating within nitrile's property limits (petroleum oil contact, temperatures below 120 °C, no food-contact requirement), nitrile provides significant cost savings.

Application Selection Guide

Contact us to discuss your specific sealing application and request silicone or nitrile samples.