EPDM (ethylene propylene diene monomer) and Viton (the trade name for FKM fluoroelastomer) are nearly mirror-image sealing materials. EPDM is specified for water, steam, polar fluids and outdoor exposure; Viton (FKM) is specified for oils, fuels, hydrocarbons and high-temperature service. They fail in each other's service environments, so choosing the wrong one produces a rapid, predictable failure.
Quick answer: EPDM: −50°C to +150°C continuous; compatible with hot water, steam, glycol brake fluid, Skydrol (phosphate-ester), dilute acids/alkalis and polar solvents; incompatible with mineral oils, hydrocarbon fuels and aromatic solvents. Viton (FKM): −20°C to +200°C continuous; compatible with mineral oils, fuels, aromatics, chlorinated hydrocarbons and strong acids; incompatible with hot water/steam, ketones, amines and Skydrol. Rule: petroleum-based fluid → FKM (Viton); water-based fluid → EPDM. EPDM is also the lower-cost option.
What Is EPDM?
EPDM is a terpolymer of ethylene, propylene and a diene. Its main chain is fully saturated, which is why EPDM resists ozone, UV, weathering and polar fluids such as water and steam. EPDM is the standard material for:
- Hot water and steam service (to +150°C)
- Glycol-based brake fluid systems (DOT 3/4/5.1)
- Outdoor electrical enclosures and HVAC
- Pharmaceutical and food-processing seals
- Dilute acids, alkalis, ketones and alcohols
EPDM's hard limit: it swells badly in petroleum oils, hydrocarbon fuels and aromatic solvents — mineral oil, gasoline and diesel destroy EPDM.
What Is Viton (FKM)?
Viton is the Chemours (formerly DuPont) trade name for FKM, the ASTM D1418 designation for fluorocarbon rubber. FKM contains 66–70% fluorine by weight, giving it exceptional resistance to oils, fuels, aromatic hydrocarbons and strong acids, plus continuous service to +200°C. Viton (FKM) is the standard material for:
- Aerospace and automotive fuel systems
- Chemical-processing seals and strong acids
- High-temperature engine and transmission seals
- Vacuum applications
FKM's hard limit: hot water and steam attack FKM (dehydrofluorination above roughly +100°C), and it fails in ketones, esters, amines and phosphate-ester (Skydrol) hydraulic fluids.
EPDM vs Viton Comparison Table
| Property | EPDM | Viton (FKM) |
|---|---|---|
| Continuous temperature | −50°C to +150°C | −20°C to +200°C |
| Mineral oil / fuels | Incompatible — swells | Excellent |
| Hot water / steam | Excellent | Poor — dehydrofluorination |
| Glycol brake fluid (DOT 3/4) | Excellent — standard | Unusable |
| Skydrol (phosphate-ester) | Compatible | Not compatible (standard FKM) |
| Ketones, esters, amines | Good | Poor |
| Ozone / UV / weather | Excellent | Good |
| Strong acids | Dilute only | Excellent |
| Relative cost | Lower | Higher |
When to Use EPDM
Choose EPDM when the seal sees:
- Water, steam, or hot-water service
- Glycol-based brake fluid
- Outdoor exposure (ozone, UV)
- Polar solvents, dilute acids or alkalis
- Skydrol / phosphate-ester hydraulic fluid
When to Use Viton (FKM)
Choose Viton (FKM) when the seal sees:
- Petroleum oils, gasoline, diesel, or lubricants
- Aromatic or chlorinated hydrocarbons
- Strong acids or aggressive chemicals
- Sustained temperatures above +150°C
Do Not — Common Specification Mistakes
- Do not put EPDM in mineral oil, gasoline, diesel, or hydraulic oil — it swells and fails.
- Do not put Viton (FKM) in hot water or steam above roughly +100°C — it degrades.
- Do not specify standard FKM for glycol brake fluid — use EPDM.
- Do not specify standard FKM for Skydrol — use EPDM, butyl, or specialty aerospace FKM.
Simple Rule
Petroleum-based fluid → Viton (FKM). Water-based fluid → EPDM.
For steam, hot water, brake fluid, or outdoor weathering, EPDM is the correct and lower-cost choice. For oil, fuel, chemical, or high-temperature service, Viton (FKM) is required. Verify a specific fluid with the chemical compatibility tool before ordering.
Frequently Asked Questions
Q1: Is EPDM or Viton better for steam?
EPDM is the correct choice for saturated steam and hot water. Viton (FKM) degrades via dehydrofluorination in hot water and steam above roughly +100°C.
Q2: Can EPDM be used with oil?
No. Mineral oil, gasoline, diesel, and hydrocarbon fuels swell and degrade EPDM. Use Viton (FKM), NBR, or HNBR for petroleum service.
Q3: Is Viton better than EPDM overall?
Not necessarily. Viton costs more and is the right choice for oil/fuel/high-temperature service, but EPDM outperforms it in water, steam, brake fluid, and outdoor weathering — and costs less. Selection depends on the fluid, not a universal ranking.
Q4: Which handles brake fluid, EPDM or Viton?
EPDM. Glycol-based brake fluids (DOT 3/4/5.1) attack FKM. EPDM is the standard brake-system material.
Q5: What temperature range do EPDM and Viton cover?
EPDM: −50°C to +150°C continuous. Viton (FKM): −20°C to +200°C continuous.
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Need EPDM or Viton (FKM) O-rings? Request a quote with your fluid, temperature and size, or contact our engineering team for material selection. We supply EPDM and FKM O-rings in AS568, ISO 3601 and DIN 3771 sizes with short lead times.
Related: EPDM O-rings | FKM (Viton) O-rings | EPDM vs Silicone | Chemical compatibility tool