EPDM and silicone are the two rubber families that dominate sealing applications across fenestration, HVAC, access systems, and data center infrastructure. They look alike on a cut cross-section. They feel similar in the hand. They both come in the same 40A to 80A durometer range and the same bulb, D, P, and compression profiles. But they are fundamentally different polymers, and picking the wrong one for your application is one of the most common and expensive specification mistakes in OEM component sourcing.
If your current supplier quoted you silicone for an application that could run EPDM, you are probably paying 40 to 60 percent more than you need to. On the other hand, if a designer spec'd EPDM for an application that actually needs silicone, you are going to see compression set, cracking, and warranty returns inside the first two years.
This guide is a decision framework. We will cover what each polymer actually is, where their performance windows differ, and how to match the right material to your application -- with specific temperature ranges, chemical compatibility notes, and durometer guidance. We will close with a decision table and an FAQ that addresses the questions engineers ask us most often when we are scoping new programs.
What EPDM and Silicone Actually Are
EPDM stands for Ethylene Propylene Diene Monomer. It is a synthetic rubber built from three monomers: ethylene, propylene, and a small amount of a diene that provides crosslinking sites for vulcanization. The result is a carbon-hydrogen backbone with no oxygen in the main chain, which is the reason EPDM shrugs off water, steam, and polar chemicals the way it does.
Silicone rubber is chemically a completely different animal. Its backbone is a chain of alternating silicon and oxygen atoms -- a siloxane backbone -- with organic side groups (usually methyl) attached to each silicon. That inorganic backbone is why silicone survives temperature extremes that shred organic rubbers, and why it behaves predictably at -60°C and at +230°C.
You do not need to carry the chemistry into every conversation with your supplier, but the polymer structure explains every performance difference that follows. EPDM is an organic rubber with a carbon backbone. Silicone is an inorganic rubber with a silicon-oxygen backbone. That is why their temperature curves, chemical compatibilities, and cost structures diverge the way they do.
Temperature Performance Head to Head
Temperature range is usually the first filter engineers apply when picking between EPDM and silicone. The numbers below are the continuous operating ranges most OEMs design against. Short-duration peaks can exceed these numbers, but continuous service beyond them will shorten the life of any seal.
| Metric | EPDM | Silicone |
|---|---|---|
| Continuous low temperature | -40°C (-40°F) | -60°C (-76°F) |
| Continuous high temperature | +120°C (+248°F) | +230°C (+446°F) |
| Intermittent peak high | +150°C (+302°F) | +260°C (+500°F) |
| Brittle point | Around -50°C | Around -90°C |
| Thermal stability (long-term) | Degrades above 125°C | Stable to 200°C continuous |
What the range actually tells you
If your application stays between -40°C and +120°C, EPDM is fully qualified on temperature alone and will cost significantly less. Silicone only starts to pull ahead when the application crosses into sub-zero extremes or above 120°C continuous. Exhaust paths, oven doors, and process equipment are silicone territory. Exterior weatherstripping, window glazing, and ambient-temperature damper seals are EPDM territory.
Weather, UV, and Ozone Resistance
Both polymers are durable outdoors, but they excel at slightly different aspects of weathering. Understanding which one matters for your application prevents specification mistakes.
EPDM has exceptional ozone and weather resistance. The saturated backbone has no double bonds for ozone to attack, which is the reason EPDM is the default choice for automotive weatherstripping, exterior window glazing gaskets, and motorized screen bottom seals. In ambient outdoor service -- UV plus ozone plus temperature cycling plus rain -- EPDM can run 15 to 25 years without meaningful degradation.
Silicone outperforms EPDM on UV resistance specifically and on high-heat aging. In extreme sun exposure at elevated temperatures, silicone holds durometer and color better than EPDM over very long timeframes. The catch is that in ambient outdoor service, both materials last longer than most of the products they are installed on, so the UV advantage rarely shows up as a practical benefit in fenestration or shading applications.
For exterior applications in normal climates, EPDM is the winner on cost and delivers performance that lasts longer than the product it seals. For exterior applications combined with high heat (solar thermal collectors, industrial enclosures on hot rooftops), silicone earns its price premium.
Chemical and Fluid Compatibility
This is where the two materials diverge the most, and where picking wrong causes the fastest failures. EPDM and silicone have almost opposite chemical compatibility profiles.
EPDM handles polar fluids exceptionally well. Water, steam, glycol (including antifreeze), brake fluid, and dilute acids and bases do not attack it. EPDM is the default hose material in automotive cooling systems for exactly this reason. What EPDM does NOT handle is petroleum products. Oils, fuels, hydraulic fluids, and greases will swell EPDM rapidly and ruin the seal. If your application involves contact with any hydrocarbon fluid, EPDM is the wrong choice.
Silicone handles temperature extremes and has good resistance to water and most polar fluids, but it is softer, tears more easily, and has limited resistance to concentrated acids, fuels, and aromatic solvents. Silicone is the default for food and medical applications (FDA 21 CFR 177.2600 compliant silicone grades are standard) because it is physiologically inert, but it is not a general-purpose chemical seal.
The quick rule: if your seal touches water, steam, glycol, or air -- EPDM. If it touches petroleum fluids or extreme temperatures -- neither EPDM nor silicone, consider Viton, NBR, or FKM. If it touches air at extreme temperature or food contact -- silicone.
Durometer, Compression Set, and Physical Properties
Both EPDM and silicone are commonly specified in the 40A to 80A Shore durometer range, which covers the vast majority of OEM compression seal, bulb seal, and gasket applications. Inside that range, neither polymer has an inherent hardness advantage -- you can order either in 50A or 70A and get usable physical properties.
Where they differ is in the supporting physical metrics.
| Property | EPDM | Silicone |
|---|---|---|
| Typical durometer range | 40A - 80A | 40A - 80A |
| Tensile strength | 7 - 20 MPa | 4 - 10 MPa |
| Elongation at break | 300 - 500 percent | 200 - 700 percent |
| Tear resistance | Good to excellent | Fair to good |
| Compression set (70 hrs @ 100°C) | 15 - 25 percent | 10 - 20 percent |
| Cold compression set | Higher than silicone | Excellent |
| Abrasion resistance | Good | Fair |
Compression set is the metric that matters most
For static sealing applications where the seal is installed once and expected to hold for years without being replaced, compression set is often the most important performance metric. Silicone edges out EPDM here, particularly at cold temperatures, which is one of the few places silicone earns its price premium even in moderate-temperature applications.
Cost Comparison
Raw material cost is the single biggest reason engineers default to EPDM when they can get away with it. For an equivalent extruded profile and durometer, EPDM is typically 40 to 60 percent less expensive than silicone. The gap widens when you get into custom tooling, because silicone is harder to extrude cleanly and requires more careful cure control.
Across the fenestration, access systems, and conveyor industries we serve, the pattern is consistent: EPDM dominates because it is cheap enough to use generously, and the applications are ambient-temperature enough that silicone's temperature advantages do not translate to real-world durability gains. Silicone wins in HVAC high-heat applications, certain food and medical applications, and specific industrial sealing environments where temperature or chemistry forces the issue.
A frequent question we get: "Why is my current supplier using silicone when EPDM would work?" There are three legitimate answers and one illegitimate one. The legitimate answers: (1) the original spec was written without a cost review and nobody ever revisited it, (2) the supplier runs a silicone line and offers it as default, (3) the application has a specific requirement that showed up after the original spec was written. The illegitimate answer: the supplier's margin is better on silicone. If you suspect the last case, run a second-source quote on the equivalent EPDM profile and see if performance requirements actually force silicone.
Four Applications, Four Decisions
Here are four real application categories and the material we would recommend for each, with reasoning.
Window glazing gasket, residential or commercial fenestration. EPDM wins. The application is ambient temperature, outdoor, ozone and UV-exposed, with no chemical contact beyond rainwater. EPDM gives you 20-plus years of service at roughly half the material cost of silicone. No real upside to silicone here.
High-temperature oven door seal, commercial kitchen equipment. Silicone wins by requirement. Continuous service above 200°C is well outside EPDM's range. The seal will take compression set and harden quickly on EPDM. Silicone is the only practical choice -- platinum-cured food-grade silicone meets FDA requirements as well.
Exterior motorized screen weatherstrip, mounted in an aluminum bottom bar. EPDM wins on cost plus UV. Ambient temperature exterior service, compression-mounted, occasional rain contact. EPDM handles every load the application presents and costs significantly less. Silicone would survive the same environment but would not outlast the screen fabric or the motor, so the extra cost buys nothing.
HVAC damper blade seal in a 200°C exhaust duct, industrial process application. Silicone required. Continuous service at 200°C is beyond EPDM's stable range, and the seal will crack and lose compression within months on EPDM. Silicone handles 200°C comfortably for extended service life and is the only correct call.
A Decision Table You Can Use at Your Desk
If you want a single reference to keep by your keyboard, this is it. Start at the top of the table and work down -- the first row that matches your application usually determines the material choice.
| Condition | EPDM | Silicone | Winner |
|---|---|---|---|
| Continuous above 125°C | Degrades | Stable | Silicone |
| Continuous below -50°C | Brittle | Flexible | Silicone |
| Contact with petroleum fluids | Fails fast | Limited resistance | Neither (use Viton/NBR) |
| Contact with water, steam, glycol | Excellent | Good | EPDM |
| Ambient outdoor, UV exposure | Excellent | Excellent | EPDM on cost |
| Ozone-heavy environment | Excellent | Good | EPDM |
| Food contact application | Some grades | FDA grades standard | Silicone |
| High-cycle compression sealing | Good | Excellent | Silicone |
| Cost sensitivity on bulk volume | Lower cost | Higher cost | EPDM |
| Abrasion and tear environment | Better | Lower | EPDM |
Frequently Asked Questions
Can I substitute one for the other in an existing product?
Sometimes. If the application is inside both materials' performance windows -- ambient temperature, no petroleum contact, no extreme chemistry -- you can usually switch EPDM to silicone or vice versa without redesign, as long as the profile and durometer match. The substitution that almost always makes sense is silicone to EPDM on ambient-temperature applications where nobody ever pressure-tested the original material choice. The substitution that almost never makes sense is EPDM to silicone without a specific temperature or chemistry reason, because you are just paying more for the same result.
Which one lasts longer outdoors?
In ambient temperate climates, both will outlast the product they seal. EPDM typically delivers 15 to 25 years in exterior weatherstrip service. Silicone delivers similar or slightly longer service life but costs significantly more. The practical answer for fenestration, shading, and access systems is that EPDM wins on cost with equivalent real-world durability. Silicone only pulls ahead in hot-climate rooftop applications or at elevated service temperatures.
Why does my current supplier use silicone when EPDM would work?
Three common reasons: the original spec was written without a cost review and nobody revisited it; the supplier's line runs silicone by default; or there is a historical application-specific requirement that nobody documented. If you are paying a silicone price on an ambient-temperature application with no chemistry requirement, get a second-source quote on the equivalent EPDM profile -- the savings are usually real.
What durometer should I specify?
For compression seals (bulb, D-shape, P-strip), 50A to 70A is the sweet spot. Softer durometers (40A) seal better at low compression but compression set faster. Harder durometers (70A-80A) hold shape longer but need more installation force to compress. For fenestration glazing gaskets, 60A to 70A is standard. For HVAC damper blade seals, 50A to 60A is typical. If you are not sure, start at 60A and adjust after the verification sample.
Do you offer both EPDM and silicone in the same profile?
Yes -- for most standard profiles (bulb, D-shape, P-strip, glazing gasket, fin seal) we can quote either material on the same tooling. That makes it easy to run a cost comparison between the two. For custom profiles, the tooling is shared as well, so the only cost difference is the raw material and the extrusion run parameters.
What should I include in an RFQ for a rubber seal?
Profile shape (with dimensions), material (EPDM, silicone, or "whichever is appropriate for the application"), durometer, color, total linear footage, and a one-line description of the application environment (interior/exterior, temperature range, chemistry exposure). If you have a sample, send it -- a physical sample eliminates half the questions on the first pass.
Not sure which material your application needs?
Send us the application details or a sample of your current part. We will recommend the right material, quote both options if it is a close call, and produce a free verification sample before you commit to a production run. No obligation, no design changes required.