EPDM and silicone are two of the most common rubbers for seals, gaskets, grommets and tubing. They look alike on a shelf. They behave very differently in service. Here is how to tell which one fits your part.
What each material is
EPDM (ethylene propylene diene monomer) is a synthetic rubber known for good resistance to weather, ozone, water, steam and many polar fluids. Silicone is a rubber built on a silicon-oxygen backbone. It stays flexible across a very wide temperature range and is used where heat or cold, or a clean material, is the main concern.
Where EPDM is the better choice
- Outdoor exposure. EPDM handles sunlight, ozone and weather well. See our page on ozone and rubber deterioration.
- Water and steam. It is widely used for water seals, coolant hoses and similar parts.
- Tear and abrasion. EPDM generally holds up better than silicone when a part is flexed, pulled or rubbed.
- Cost. EPDM is usually the lower-cost option for a general-purpose seal.
Where silicone is the better choice
- Temperature extremes. Silicone stays flexible at low temperatures and keeps working at high temperatures where many rubbers harden.
- Clean applications. Compounds are available for food, medical and similar uses, subject to the grade and the applicable requirements.
- Electrical parts. Silicone is a common choice for insulating boots and seals.
What neither one does well
Neither EPDM nor silicone is a good match for petroleum oils and fuels. EPDM swells in oil. Silicone can swell and lose strength in many fuels and oils. If your part touches oil, fuel or hydraulic fluid, ask us about a different compound, and see how oil exposure is checked in our ASTM D471 liquid immersion page.
A simple rule of thumb
If the part lives outdoors or around water and steam, start with EPDM. If it has to survive a wide temperature swing or needs a clean-grade material, start with silicone. If oil or fuel is involved, start with neither, and talk to us first. A short call about your fluids and temperatures can save a failed prototype and a second tooling round.
Hardness also changes the picture. A softer compound seals easily at low clamp force but can be damaged during assembly. A harder compound resists extrusion but needs more force to seat. Choose the material first, then tune the hardness to the joint.
How to choose
- List the fluids the part will touch, including cleaners.
- Give the real minimum and maximum temperature, not just the nominal one.
- Note whether the part is outdoors, flexed, or under constant compression. Compression set matters for seals, see what is compression set.
- State the hardness you need and how it will be checked, see our ASTM D2240 hardness page.
Read more about the materials we mold, our moldaje de goma personalizado and our full list of Capacidades.
Have a part that needs to hold its shape or pass a spec? Send the drawing or sample requirements to estimator@coirubber.com and our engineering team will review it. Coi Rubber has been in business since 2003, is US owned and operated, and our Wuhu, China manufacturing facility is IATF 16949 certified.