EPDM vs Viton (FKM) Rubber
EPDM and FKM sit at opposite ends of the elastomer range. EPDM is the economical specialist for water, steam, and weather, but it fails in oils and fuels. FKM, the fluoroelastomer sold under trade names like Viton, is the premium choice for aggressive chemicals, fuels, and high heat to about 200°C, at several times the cost. The two rarely suit the same job: the deciding factors are the fluid and the temperature.
These materials are often weighed against each other for seals and o-rings when engineers are unsure how aggressive the environment really is. This guide compares them property by property so you specify the right one, and do not overpay for FKM when EPDM would do, or under-spec EPDM where FKM is required. Wayne Rubber molds and custom formulates both from our Wixom, Michigan plant.
Viton and FKM: A Note on Naming
Viton is a registered trade name for a family of fluoroelastomers, now owned by Chemours. The generic ASTM D1418 designation for the material is FKM. Because FKM is not a single compound but a family of grades (Type A, B, F, GF, GLT) with different fluorine contents and chemical profiles, the correct way to specify one is by FKM grade type and fluorine content, not by trade name. This page uses “FKM” throughout, and “Viton” only where it helps match how the material is commonly searched. When you send a spec, an FKM grade type tells us exactly what you need.
Quick Comparison
| Property | EPDM | FKM (Viton type) |
|---|---|---|
| Continuous service temperature | -40°C to +150°C | -20°C to +200°C (specialty grades wider) |
| Petroleum oil and fuel resistance | Poor. Swells and degrades | Excellent |
| Aggressive chemical / solvent resistance | Poor to fair | Excellent |
| Water, steam and glycol coolant | Excellent | Fair. Poor in hot water and steam |
| Ozone, UV and weathering | Excellent | Excellent |
| Low temperature flexibility | Excellent | Fair (standard grades) |
| Flame resistance | Poor | Good. Self-extinguishing |
| Post-cure required | No | Yes, to reach full properties |
| Relative compound cost | Low | High (several times EPDM) |
| Typical hardness range | 40 to 90 Shore A | 60 to 90 Shore A |
The Two Materials
What Is EPDM Rubber?
EPDM (ethylene propylene diene monomer) is a synthetic elastomer with a fully saturated polymer backbone that resists ozone, UV, and oxidation, making it the benchmark for outdoor, water, and steam service. It does not swell in water and stays flexible to low temperatures. Its weakness is petroleum: oils, fuels, and greases destroy it. It is also one of the cheapest elastomers available. Full data is on the EPDM rubber material page.
What Is FKM (Viton) Rubber?
FKM is a fluoroelastomer built around carbon-fluorine bonds, among the strongest in organic chemistry. That backbone gives FKM two properties no hydrocarbon rubber can match: thermal stability to roughly 200°C continuous and near-inertness to fuels, oils, acids, and many solvents. It is the premier sealing material for the harshest environments, at a premium price, and standard grades are post-cured to reach full properties. See the FKM material page.
Property by Property
Chemical, Fuel and Oil Resistance
This is the clearest divide. FKM resists petroleum fuels, oils, acids, and aromatic and chlorinated solvents that would rapidly destroy EPDM. EPDM’s resistance to hydrocarbons is poor. If the part contacts fuel, oil, or aggressive chemicals, FKM is the answer, with the specific grade chosen for the exact chemistry. One reversal worth knowing: EPDM outperforms FKM in certain polar fluids such as brake fluids, hot water, and steam.
Temperature Range
FKM handles higher continuous heat, to about 200°C, and specialty grades go higher. EPDM tops out near 150°C. On the cold end, standard EPDM stays flexible better than standard FKM, though low-temperature FKM grades (such as GLT) narrow that gap.
Water, Steam and Coolant
EPDM wins decisively. It is the dominant material in cooling systems, water infrastructure, and steam. FKM is only fair in hot water and steam and can degrade over long exposure, so it is rarely chosen for aqueous service unless chemicals are also present.
Weathering and Ozone
Both are excellent. Neither cracks from ozone or UV, so weathering alone does not separate them. The decision comes back to fluids, temperature, and cost.
Cost and Processing
EPDM is one of the most economical elastomers; FKM is several times more expensive per pound. FKM also requires a post-cure step to develop its full compression set and heat resistance, adding process cost. Specifying FKM where EPDM would survive is a common and expensive over-spec. Specifying EPDM where fuel or chemicals are present is an under-spec that fails in service. Matching material to environment is where custom formulation pays off.
Typical Applications
Choose EPDM for: coolant and water-system seals and hoses, molded gaskets and seals in water or steam service, weatherstripping and outdoor sealing, HVAC gaskets, brake-fluid seals, and cost-sensitive oil-free parts.
Choose FKM for: fuel system o-rings and seals, chemical processing gaskets, high-temperature under-hood and turbocharger components, aerospace and oil-and-gas sealing, and any part exposed to aggressive solvents or sustained heat.
How to Choose in 30 Seconds
- Is there fuel, oil, or an aggressive chemical or solvent? Yes: FKM (grade matched to the chemistry).
- Is it water, steam, coolant, or brake fluid? Yes: EPDM.
- Does it run above 150°C? Yes: FKM.
- Is it outdoor and oil-free, and cost matters? EPDM.
- Both chemicals and very low temperatures? Ask about low-temperature FKM grades.
- Not sure how aggressive the environment is? Send us the fluid, temperature, and drawing. We will recommend a material and grade. Contact Wayne Rubber.
Frequently Asked Questions
Is Viton better than EPDM?
Not overall. FKM (Viton) is better for fuels, oils, aggressive chemicals, and high heat. EPDM is better for water, steam, coolant, and brake fluid, and it costs far less. FKM is a premium material, so it is only “better” where its chemical and heat resistance are actually required.
What is the difference between Viton and FKM?
They are the same class of material. FKM is the generic ASTM D1418 designation for fluoroelastomer; Viton is a registered trade name for FKM grades. The correct way to specify is by FKM grade type and fluorine content rather than by trade name.
Can EPDM be used with oil or fuel?
No. EPDM swells and degrades in petroleum oils and fuels. Use FKM for fuel and chemical service, or nitrile (NBR) for general oil sealing at lower cost and temperature.
Why is EPDM used for coolant and brake systems instead of Viton?
EPDM resists water, glycol coolant, and glycol-based brake fluids that degrade FKM. In these polar-fluid environments EPDM is the correct and lower-cost choice, which is why FKM is reserved for petroleum fuels and aggressive chemicals.
How much more expensive is FKM than EPDM?
FKM compounds cost several times more per pound than EPDM and also require a post-cure step. Because of this, FKM should be specified only where fuel, chemical, or high-temperature exposure genuinely requires it, and EPDM used wherever the environment allows.
Not Sure If You Need FKM or EPDM?
Over-specifying FKM wastes money; under-specifying EPDM fails in service. Send us the fluid, temperature, and drawing, and our engineers will recommend the right material and grade. Molding and compounding from our Wixom, Michigan plant.
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