EPDM O-Rings

EPDM is the elastomer you reach for when the fluid is water and the enemy is the weather. The name spells out the recipe: ethylene, propylene, and a diene third monomer, present at up to 12 percent and most often norbornene. The ethylene and propylene build a saturated, non-polar backbone with nothing for oxygen and ozone to grab onto. The diene adds back just enough unsaturation to give the cure system somewhere to cross-link.

That backbone is the entire story of the material, good and bad. It is why Freudenberg calls EPDM vulcanizates “outdoor materials” and the material of choice for sealing profiles in the automotive and construction industries. It is why EPDM owns potable water, steam, and glycol brake fluid. And it is why EPDM turns into a swollen, useless ring the moment it meets petroleum oil. There is no grade, no durometer, and no cure system that fixes that. Get the fluid right and EPDM will outlive the equipment. Get it wrong and it fails in a weekend.

Quick specs

Common names

Drawings and catalogs call this family a half dozen things. These all land in the same neighborhood:

• EPDM, the ASTM D1418 designation, ethylene-propylene-diene rubber
• EPR, ethylene propylene rubber, used loosely for the whole family
• EPM, the ethylene-propylene copolymer with no diene at all, a real and separate material covered further down
• Ethylene propylene diene monomer, the long-form spelling out of EPDM

Mechanical properties

• Outstanding resistance to ozone, ageing, and weathering. This is the property that earns EPDM its “outdoor material” reputation, and it is not marginal, it is categorical.
• Excellent hot water and steam resistance, which is why it goes into water-bearing components and products in contact with water and aqueous foodstuffs.
• Excellent glycol resistance, which is what makes it the brake-fluid seal.
• Good compression set resistance, best in peroxide-cured grades.
• Good electrical insulating properties.
• Strength and low-temperature flexibility both track ethylene content, and they pull in opposite directions. More on that below.
• Effectively unlimited shelf life. A saturated backbone has nothing to age.

Limitations

This is the honest list, and the first item is not a nuance. It is the single most common sealing mistake we see across the counter:

• NEVER petroleum oil, grease, fuel, or gasoline. EPDM is unstable in mineral oils and greases and in gasoline. It swells, softens, loses all sealing force, and dies. If you have an O-Ring that came out fat, mushy, and oversized after a short run in oil, you almost certainly installed EPDM where nitrile belonged. See chemical swell or shrink for what that failure looks like, then use Nitrile (Buna-N) or FKM (Viton®) instead.
• Not for aliphatic, aromatic, or chlorinated hydrocarbons. Same mechanism, same result. Solvents, degreasers, and hydrocarbon process streams are all out.
• Not for hot concentrated acids. EPDM handles dilute acids and bases well, but concentration and heat together will take it apart.
• Not the high-pressure dynamic champion. For rod and piston duty with real pressure behind it, polyurethane has the tear strength, extrusion resistance, and abrasion life that EPDM does not.
• Heat ceiling around +300°F. Above that, step to silicone or FKM (Viton®), but check the fluid first. Neither of those is a drop-in for EPDM in steam or brake fluid, and swapping compounds to chase temperature while ignoring media is how good seals get replaced by worse ones.

Chemical compatibility

Handles well:

• Hot and cold water, steam, and aqueous foodstuffs
• Glycol ether-based brake fluids (DOT 3, 4, 5.1)
• Washing lyes and detergents
• Oxidizing media
• Acids and bases, in reasonable concentrations
• Polar organic media, including ketones
• Phosphate-ester hydraulic fluids (Skydrol®), in the right grade
• Ozone, UV, sunlight, and weather

Attacks it:

• Mineral oils and greases
• Gasoline and fuels
• Aliphatic hydrocarbons
• Aromatic hydrocarbons
• Chlorinated hydrocarbons

The pattern is worth memorizing because it is so clean: EPDM likes polar fluids and hates non-polar ones. Water, glycol, ketones, and phosphate esters are friends. Anything that came out of a barrel of crude is not. Confirm your exact fluid on the Chemical Compatibility page or in the interactive Chemical Compatibility Chart.

A word on temperature ranges

Our published range for EPDM is -65°F to +300°F (-54°C to +149°C), and that is a fair headline for the compounds we stock. It is also an approximation, because EPDM is a family and the ends of the range move with the recipe:

• Ethylene content sets the cold end. The higher the ethylene content, the higher the strength and the lower the flexibility at low temperatures. Above roughly 60 percent ethylene the polymer can begin to crystallize. Cold-flexible grades give up some strength to get there.
• Cure system sets the hot end. Peroxide-cured grades hold up better at the top of the range, and noticeably better in steam and in compression set, than sulfur-cured grades. A sulfur-cured general-purpose compound will not see +300°F for long.
• Freudenberg publishes +302°F for its EPDM materials, close to the commercial norm.

As always, a published range assumes the compound, the media, the pressure, the hardware, and the duty cycle all cooperate. Continuous steam at the top of the range is a very different ask than dry air at the same temperature. If you are sitting near an edge, send us the conditions and we will pull the datasheet for the actual compound instead of guessing from a chart.

Shop EPDM O-Rings

Every EPDM variation we stock, by grade and size:

Inch (AS568):

• EPDM FDA Grade (abrasion-resistant)
• EPDM FDA & NSF-61 (chloramine-resistant, peroxide-cured)
• EPDM 80 Duro (Simrit E454, NAS-1611, peroxide-cured)

Metric:

• EPDM Metric (EPR / EPM)

Not sure which size you need? Start at the size charts or the master size chart. Need a durometer, color, or approval that is not listed? Ask us.

Variations and grades explained

EPDM is not one material. The label on the bag tells you very little until you know how it was cured and what is in it.

By cure system

This is the biggest lever in EPDM performance, bigger than durometer, bigger than anything else on this list.

If the job involves steam, drinking water, food contact, or phosphate esters, assume peroxide and confirm it. If it is a gasket around a hose clamp in the sun, sulfur-cured is money well saved.

By ethylene content

The ethylene-to-propylene ratio is the compounder’s dial for strength versus cold. More ethylene means more strength and less flexibility when it gets cold, with crystallization possible above about 60 percent. Less ethylene means a softer, more cold-tolerant compound. The -65°F end of our published range belongs to the lower-ethylene side of the family.

By hardness (durometer)

• 70 Shore A: the standard for most water, steam, and weather sealing.
• 80 Shore A: firmer, for higher pressure and better resistance to extrusion and nibbling through the gland gap.

If you are pushing pressure and thinking about going harder, look at the gland first. See groove design.

EPM vs EPDM

EPM is the ethylene-propylene copolymer with no diene component at all. It is widely used, though mostly outside of O-Rings: its main jobs are oil additivation and impact modification of thermoplastics. Without the diene there are no unsaturated sites for a sulfur cure, so EPM has to be peroxide cured. On a catalog page you will often see “EPR / EPM” used loosely alongside EPDM. For a molded O-Ring, what you are almost always buying is EPDM.

FDA and NSF-61 grades

• FDA grade: compounded from FDA-listed ingredients for incidental food and beverage contact. See FDA 21 CFR 177.2600.
• NSF-61 grade: certified for potable water system components. The chloramine-resistant, peroxide-cured compound we stock is built for the disinfectants municipal water systems actually run. See NSF/ANSI 61.

Aerospace phosphate-ester grades

EPDM is the standard elastomer for Skydrol® and other phosphate-ester aviation hydraulic fluids, which destroy nitrile. Those parts are called out to NAS1613 and NAS1611. The Simrit® E454 peroxide-cured 80 duro compound we stock is a Freudenberg brand built to NAS-1611. See the mil-spec and aerospace reference.

Standards and specifications

EPDM O-Rings are supplied across the full AS568 inch size range and common metric sizes. The callouts that matter:

• ASTM D1418: designates the polymer as EPDM.
• ASTM D2000 / SAE J200: the line-callout system most commercial EPDM is bought to.
• NSF/ANSI 61: certification for potable water system components. See NSF-61.
• NAS1613 and NAS1611: the aerospace standards for phosphate-ester hydraulic service. See mil-specs.
• FDA 21 CFR 177.2600: the rubber article rule for repeated food contact. See FDA food contact.

If your drawing calls out a specific spec or compound, tell us and we will match it, with a Certificate of Conformance and lot traceability under our ISO 9001:2015 system.

Typical applications by industry

See O-Rings by Industry for the wider picture, or Design & Engineering for the gland around the seal.

Is EPDM the right choice?

Three questions settle it:

1. Is there any petroleum oil, grease, or fuel in the system? If yes, stop. EPDM is wrong no matter how good the rest of the fit looks. Go to nitrile or FKM.
2. Is the fluid water, steam, glycol, or a phosphate ester? If yes, EPDM is very likely the answer, and probably a peroxide-cured one.
3. Does it live outside? Sun, ozone, and weather are where EPDM beats nearly everything else in the catalog at nearly any price.

That first question does most of the work. EPDM is not a compromise material, it is a specialist, and specialists are excellent right up until you hand them the wrong job.

Not sure whether EPDM covers your fluid and temperature? Send us the conditions: the media, the temperature, the pressure, and whether the seal moves. We will spec the compound and the size with you. We make getting O-Rings easy.

Polymer composition, diene content, ethylene content effects, EPM, ozone and weathering behavior, glycol and brake fluid service, hot water and steam service, media resistance and instability list, and the +302°F figure: Freudenberg FST 2025 Technical Manual, ch. 2 (Materials and Process Engineering), §3.4, p. 55. Commercial grade ranges reflect the wider EPDM market. The datasheet for your specific compound always governs; test parts in your actual service conditions before committing to a critical seal.