Compound Library
O-Ring & Seal Materials
Material selection is the single most critical design decision in any sealing application. The right compound ensures reliable performance; the wrong one leads to premature failure, leakage and unplanned downtime. FITCO compounds and molds across eleven core elastomer and fluoropolymer families — each matched to specific fluid, temperature and regulatory requirements.
NBR (Nitrile / Buna-N)
NBR is the workhorse elastomer of the sealing industry — a copolymer of butadiene and acrylonitrile (ACN). Standard grades (18–22% ACN) offer good low-temperature flexibility, while high-ACN grades (38–50%) deliver superior oil and fuel resistance at the expense of cold flexibility. It is the most widely specified O-ring material across hydraulic systems, fuel-handling equipment, automotive fluid circuits and general industrial sealing. NBR provides excellent compression set resistance and is cost-effective for high-volume production.
Applications: Hydraulic cylinders, fuel-system O-rings, pneumatic fittings, automotive engine seals, gear-box seals, industrial pumps and valves.
FKM / FPM (Fluoroelastomer / Viton®)
FKM (commonly known by the trade name Viton®) is a fluorine-containing elastomer engineered for aggressive chemical and high-temperature environments. Higher fluorine content (up to 70%) increases chemical resistance and heat tolerance. FKM offers exceptional resistance to oils, fuels, ozone and most industrial chemicals, making it the go-to material where NBR falls short on temperature or chemical exposure. Compression set performance remains strong through extended service at elevated temperatures.
Applications: Oil & gas downhole seals, chemical processing equipment, fuel injector O-rings, aerospace fluid systems, semiconductor tool seals, automotive exhaust and turbocharger seals.
EPDM (Ethylene Propylene Diene Monomer)
EPDM's fully saturated polymer backbone gives it outstanding resistance to ozone ageing, UV degradation and weathering. It performs exceptionally in steam and hot-water systems and is FDA-compliant in white/food-grade formulations. EPDM is the preferred choice for potable-water seals, steam autoclaves, brake systems, and outdoor applications where long-term weather exposure is a design factor. It is incompatible with petroleum-based fluids.
Applications: Steam system seals, automotive brake systems, drinking-water fittings, outdoor electrical enclosures, HVAC systems, solar-panel mounting seals, washing-machine door gaskets.
Silicone (VMQ)
Silicone provides the widest usable continuous temperature range of any common elastomer and is available in FDA- and USP Class VI-compliant grades for food-contact and medical applications. Its flexibility at extreme cold and stability at sustained high temperatures make it ideal for static seals in ovens, autoclaves and LED lighting fixtures. Silicone has low mechanical strength compared with other elastomers, so it is best suited to static or low-pressure applications.
Applications: Medical devices, food & beverage processing, pharmaceutical equipment, LED and lighting housings, oven and autoclave door seals, baby-care products, aerospace cabin seals.
HNBR (Hydrogenated Nitrile)
Hydrogenating the NBR backbone removes most residual unsaturation, substantially improving heat resistance, ozone tolerance and mechanical strength while retaining the oil and fuel resistance of standard nitrile. HNBR bridges the gap between NBR and FKM — delivering near-FKM heat performance at a lower cost point. It is widely specified in automotive timing systems, oil & gas sour-service applications and air-conditioning systems where R134a or R1234yf refrigerants are used.
Applications: Automotive timing-belt seals, oil & gas sour-gas environments, A/C compressor shaft seals, biodiesel fuel systems, industrial rollers and belts.
FFKM (Perfluoroelastomer / Kalrez®)
FFKM replaces essentially all hydrogen atoms with fluorine, approaching PTFE-level chemical inertness while retaining the elasticity of a true rubber. It is the ultimate seal material for the most extreme chemical and thermal environments — semiconductor fabs, pharmaceutical reactors, chemical processing and deep downhole oil & gas service. FFKM commands a premium price but is often the only viable choice where no other elastomer survives the media and temperature combination.
Applications: Semiconductor wafer-fab equipment, pharmaceutical reactor vessels, aggressive chemical processing, deep oil & gas wells, paint and coatings spray equipment, nuclear applications.
Polyurethane (PU / AU / EU)
Polyurethane delivers the highest tensile strength and abrasion resistance of any elastomer used in sealing. PU seals outlast NBR by 5–10× in wear life under dynamic hydraulic duty. It is the material of choice for hydraulic rod seals, piston seals, wiper seals and buffer seals in mobile and industrial hydraulic cylinders. PU's main limitation is its low upper temperature limit — above 80 °C continuous it softens and loses properties.
Applications: Hydraulic cylinder rod and piston seals, pneumatic cylinders, wiper/scraper seals, shock absorbers, material-handling equipment, injection-moulding machines.
CR / Neoprene (Polychloroprene)
Neoprene (CR) was the first commercial synthetic rubber and remains valued for its unique combination of moderate oil resistance, good weathering/ozone resistance and inherent flame retardancy. It offers a more balanced property set than NBR (which has better oil resistance but poor ozone resistance) and is FDA-compliant in suitable grades. CR is widely used in refrigeration, marine, construction and electrical-insulation applications.
Applications: Refrigeration compressor seals, marine shaft seals, construction expansion joints, electrical cable jackets, conveyor-belt covers, automotive window seals.
ACM (Polyacrylate Rubber)
ACM is a heat- and hot-oil-resistant elastomer developed specifically for the automotive industry. It performs well in contact with engine oils containing modern additive packages at sustained temperatures up to 175 °C — conditions that would degrade standard NBR. ACM's main limitation is poor water and steam resistance, so it is not suitable for coolant or steam circuits. It is a cost-effective alternative to FKM in automotive oil-path sealing.
Applications: Automotive valve-cover gaskets, oil-pan gaskets, automatic transmission seals, crankshaft seals, timing-cover seals.
PTFE (Polytetrafluoroethylene)
PTFE is not an elastomer but a rigid fluoropolymer used in sealing as backup rings, wear rings, guide rings, and machined seals where chemical inertness and very wide temperature range are critical. Virgin PTFE has the lowest friction coefficient of any solid, making it ideal for dynamic seals. Filled grades — glass, bronze, carbon/graphite and MoS₂ — improve wear resistance, creep resistance and PV capability for different service conditions. PTFE seals require energising by an elastomer O-ring or a spring because PTFE has no inherent elasticity.
Applications: Backup rings, guide rings, piston and rod seals (spring-energised), ball-valve seats, gaskets for chemical service, bearing bushes, FDA food-contact seals.
FVMQ (Fluorosilicone)
Fluorosilicone adds trifluoropropyl side groups to the silicone backbone, giving it fuel and oil resistance that standard silicone lacks while retaining the wide temperature range. FVMQ is widely specified for aerospace fuel-system O-rings and static seals where exposure to Jet A, JP-8 and aviation gasoline must be combined with cold-soak performance at altitude (-55 °C). Like standard silicone, FVMQ has lower mechanical strength and is best suited for static or low-pressure applications.
Applications: Aerospace fuel-system seals (static), aircraft connector seals, military vehicle fuel-system O-rings, automotive fuel-injector O-rings.
Not sure which material fits?
Selection support
Use the chemical compatibility guide as a starting point, then confirm with our engineering team against your exact fluid, concentration and temperature. FITCO can also formulate custom compounds tailored to your specific application requirements — contact us with your service conditions for a recommendation.