FKM Fluoroelastomer Seals
Wayne Rubber manufactures custom FKM fluoroelastomer seals, gaskets, and o-rings for high-temperature, chemical processing, fuel system, and aggressive industrial applications. Available in Type A, B, F, and GF compound grades for compression molding, transfer molding, and injection molding to your exact dimensions.
Why FKM Fluoroelastomer for Seals?
FKM (fluoroelastomer, designated per ASTM D1418 — equivalent to FPM under ISO/DIN 1629) is the premium sealing compound for applications where standard elastomers fail: continuous service temperatures above 250°F, exposure to aggressive fuels and solvents, concentrated acids or bases, or any combination of heat and chemical attack. Its fluorine-to-carbon backbone gives it a level of chemical and thermal stability that hydrocarbon-based elastomers cannot approach.
FKM’s fluorine content — typically 66–70% by weight in standard grades — is the primary driver of its performance. Higher fluorine content increases resistance to oils, fuels, and polar solvents. The different FKM types (A, B, F, GF, GLT) vary in monomer composition, fluorine content, and curing chemistry to optimize performance for different environments.
FKM does have meaningful limitations. Its low-temperature flexibility is inferior to most other elastomers — standard grades begin to stiffen at temperatures below −15°F (−26°C). For cold-climate or cryogenic applications, GLT (low-temperature) grades push service down to −40°F (−40°C), but FKM is never the best cold-temperature choice. FKM also resists steam poorly and degrades in contact with ketones, low-molecular-weight esters, and certain amines — use our Chemical Resistance Guide to confirm compatibility with your specific media.
For environments that exceed even FKM’s capabilities — extremely aggressive chemical exposure above 400°F or near-universal chemical resistance requirements — FFKM perfluoroelastomer is the next step up.
Fluorine Content & Chemical Resistance
FKM’s exceptional chemical resistance comes directly from its fluorine-to-carbon ratio. As fluorine content increases, resistance to oils, fuels, and aggressive chemicals improves but low-temperature flexibility decreases. The chart below shows fluorine content across common elastomer families and what it means for seal performance.
FKM Seal Material Specifications
Standard FKM compound properties for sealing applications. Wayne Rubber custom formulates specialty grades for low-temperature service, base resistance, or specific chemical environments beyond the values shown here.
| Property | Standard Value / Range |
|---|---|
| Temperature Range | −15°F to +400°F (−26°C to +204°C) continuous Intermittent to +446°F (+230°C); GLT grades to −40°F (−40°C) |
| Hardness (Durometer) | 55 to 90 Shore A Standard grade: 70 or 75 Shore A |
| Fluorine Content | 66% (Type A) – 70% (Type F / GF) Higher fluorine = greater chemical and fuel resistance |
| Tensile Strength | 1,200 – 2,500 psi (compound-dependent) |
| Elongation at Break | 150% – 350% |
| Compression Set | Good to Excellent (bisphenol-cured grades superior) |
| Color | Black or brown (standard); custom colors available |
| ASTM Designation | ASTM D1418: FKM — ASTM D2000: HK (typical) |
| Petroleum Oil & Fuel Resistance | Excellent |
| Aromatic Solvent Resistance | Excellent (superior to NBR) |
| Acid Resistance | Excellent (concentrated and dilute acids) |
| Steam Resistance | Poor — not recommended for steam service |
| Ketone / Amine Resistance | Poor — not recommended; use FFKM for these environments |
| Ozone & UV Resistance | Excellent |
FKM Fluoroelastomer Grades
FKM encompasses several chemically distinct compound types, each optimized for a different balance of chemical resistance, low-temperature flexibility, and base resistance. Wayne Rubber’s in-house compounding capability allows us to supply the correct FKM type for your specific environment rather than defaulting to a single general-purpose grade.
VDF/HFP copolymer — the most common FKM grade. ~66% fluorine content. Excellent resistance to petroleum oils, fuels, hydraulic fluids, and most acids. The correct starting point for the majority of industrial and automotive FKM applications.
VDF/HFP/TFE terpolymer. Higher fluorine content (~67–69%) than Type A. Better resistance to concentrated acids, fuels, and aromatic solvents. Common in chemical processing, refinery, and fuel handling applications where Type A’s acid resistance falls short.
VDF/TFE/PMVE terpolymer. ~70% fluorine content — the highest of standard FKM grades. Maximum resistance to aggressive fuels, aromatic solvents, and highly concentrated chemicals. Used in fuel injection systems, offshore oil equipment, and chemical plant sealing.
Formulated without vinylidene fluoride (VDF) to eliminate dehydrofluorination in strongly alkaline media. Used in caustic soda, amine-based, and high-pH process environments where standard FKM grades are chemically attacked by bases.
PMVE-containing grade with improved flexibility at low temperatures — down to −40°F (−40°C). Used in cold-climate automotive, outdoor equipment, and refrigeration applications where standard FKM would harden and lose sealing force.
When FKM’s limitations — steam resistance, ketone exposure, or temperatures above 400°F — rule it out, FFKM perfluoroelastomer provides near-universal chemical resistance and service to 600°F. Learn more about FFKM →
FKM Seal Product Forms
FKM O-Rings
Available in all standard AS568, ISO 3601, Metric, and JIS B2401 sizes, as well as fully custom dimensions. FKM o-rings are the most common application of fluoroelastomer — used in hydraulic systems, fuel injectors, chemical processing valves, and any static or dynamic seal where oil and temperature resistance are simultaneously required.
Use the O-Ring Size Search to confirm your standard size, and the Gland Calculator to verify gland dimensions. Note that FKM shrinks at a different rate than NBR during molding — tooling for NBR o-rings is not directly usable for FKM. Wayne Rubber accounts for material-specific shrinkage in all custom tooling.
FKM Gaskets
Die-cut from FKM sheet stock or compression and transfer molded for complex profiles. FKM gaskets are specified wherever chemical resistance and high-temperature sealing must be achieved in a flat or flanged joint. Common in chemical plant equipment, petrochemical flanges, high-temperature fuel system joints, and valve body gaskets.
FKM Seals (Custom Molded)
Lip seals, rod seals, face seals, and specialty profiles are compression or injection molded to custom cross-sections. FKM is the material of choice for custom-molded seals in any application involving hot oil, aggressive fuel blends, or chemical exposure that rules out standard elastomers. Wayne Rubber’s engineering team reviews your gland dimensions, service conditions, and application requirements before specifying the appropriate FKM grade and mold geometry.
FKM Diaphragms
Fabric-reinforced and solid FKM diaphragms for chemical pump, valve actuator, and pressure sensing applications involving aggressive chemicals or elevated temperatures. FKM diaphragms replace NBR or EPDM where the process fluid is chemically incompatible with those materials — common in solvent pumps, chemical metering systems, and high-temperature pressure regulators.
FKM Seal Applications by Industry
FKM fluoroelastomer is the material of choice when no standard elastomer can survive the operating environment. The industries below represent the core FKM seal demand — each with distinct chemical, temperature, or pressure requirements that standard compounds cannot meet.
FKM vs. Other Seal Materials
FKM is the correct specification when the application demands both high-temperature service and aggressive chemical resistance — a combination no standard elastomer can provide. This table helps confirm FKM is the right choice, or when FFKM or a more cost-effective alternative would better serve the application.
| Property | FKM | FFKM | NBR (Nitrile) | HNBR | EPDM |
|---|---|---|---|---|---|
| Max. Continuous Temp. | +400°F (+204°C) | +600°F (+316°C) | +250°F (+121°C) | +300°F (+149°C) | +300°F (+149°C) |
| Petroleum Oils & Fuels | ✓ Excellent | ✓ Excellent | ✓ Excellent | ✓ Excellent | ✗ Poor |
| Aromatic Solvents | ✓ Excellent | ✓ Excellent | ✗ Poor | ▶ Fair | ✗ Poor |
| Concentrated Acids | ✓ Excellent | ✓ Excellent | ▶ Limited | ▶ Good | ▶ Good |
| Steam | ✗ Poor | ▶ Limited | ▶ Fair | ✓ Good | ✓ Excellent |
| Low-Temp. Flexibility | ✗ Limited (to −15°F) | ✗ Limited | ✓ Good (to −40°F) | ✓ Good | ✓ Excellent |
| Ketones / Amines | ✗ Poor | ✓ Excellent | ✗ Poor | ✗ Poor | ▶ Limited |
| Relative Cost | High | Very High | Low | Medium – High | Low – Medium |
FKM Seal Manufacturing at Wayne Rubber
In-House FKM Compounding
Wayne Rubber mixes FKM compounds in-house across Type A, B, F, GF, and GLT grades. This allows us to tailor fluorine content, curing chemistry, durometer, and compound additives to your exact application requirements rather than supplying a single off-the-shelf grade. Virgin FKM polymer from established fluoropolymer producers only — no regrind. See our full FKM material page for compound data.
Material-Specific Tooling
FKM compounds shrink at a different rate than NBR, EPDM, or silicone during curing. Wayne Rubber maintains material-specific tooling that accounts for FKM’s shrinkage characteristics, ensuring dimensional accuracy to AS568 and custom drawing tolerances. Tooling designed for other materials cannot simply be reused for FKM — we build to the material.
Compression, Transfer & Injection Molding
FKM seals are manufactured by compression, transfer, or injection molding depending on geometry, volume, and tolerance requirements. All three processes are available in-house at Wayne Rubber. Injection molding is preferred for high-precision o-rings and seals where flash control and dimensional repeatability are critical. More on our manufacturing capabilities.
Quality & Post-Cure
FKM seals require post-curing — a secondary oven cure step — to fully develop their chemical and mechanical properties and minimize compression set. Wayne Rubber performs post-cure as standard on all FKM parts, per manufacturer recommendations for each polymer grade. Every batch is tested against hardness, dimensional, and material specifications before shipment, with full certification documentation available.
Request a Quote for Custom FKM Fluoroelastomer Seals
Provide your part geometry, operating temperature, fluid exposure, and any applicable specifications. Wayne Rubber will recommend the correct FKM grade and supply a quote.