Silicone vs EPDM vs NBR: How to Choose Sealing Material
Choose the sealing material by three factors, in order: temperature, media exposure, and cost. Silicone (VMQ) wins for wide temperature ranges, food/medical contact and long-term flexibility; EPDM wins for outdoor weathering, ozone, steam and water at a lower cost; NBR (nitrile) wins for petroleum oils and fuels under moderate temperatures. If your application contacts oil — NBR or a fluorocarbon; if it sees heat, steam or food — silicone; if it lives outdoors — EPDM.
TL;DR — comparison at a glance
What Are Silicone, EPDM and NBR?
Silicone rubber (VMQ) has a silicon–oxygen backbone instead of the carbon backbone of most rubbers. That structure gives it the widest temperature range of the three, low compression set, and excellent electrical insulation and weather resistance. It is available as liquid silicone rubber (LSR) for precision injection molding and as solid silicone (HCR) for compression, transfer and extrusion molding. Silicone is the default choice for food-contact, medical, high-temperature and high-precision sealing applications.
EPDM is an ethylene-propylene-diene elastomer. Its saturated backbone resists ozone, UV, weathering, water and steam — which is why it dominates automotive weather seals, roofing membranes and outdoor gaskets. EPDM’s weakness is petroleum-based oils and fuels, which attack it.
NBR (nitrile rubber, Buna-N) is a copolymer of butadiene and acrylonitrile. The nitrile content gives it outstanding resistance to petroleum oils, fuels and greases — the reason it is the workhorse of fuel systems, hydraulic seals and oil-contact O-rings. Its weaknesses: poor ozone/UV resistance and a lower temperature ceiling.
The 3-Factor Decision Framework
1. Temperature — the first filter
Apply the continuous-service temperature of your application before anything else:
- Above 150 °C continuously → silicone. EPDM tops out around 150 °C; NBR around 120 °C.
- −30 to 120 °C with oil contact → NBR territory.
- −45 to 150 °C, no oil → EPDM covers most outdoor and water applications economically.
- Wide swings (−60 to 200+ °C) → silicone’s range is unmatched.
Remember the difference between continuous and peak temperature: most rubbers survive short peaks well above their continuous rating, but repeated peaks accelerate aging (hardening, cracking, compression set). Specify continuous service conditions in your RFQ — not just the highest number on the datasheet.
2. Media exposure — the second filter
What the seal contacts is usually the deciding factor between EPDM and NBR:
If in doubt about a specific chemical, ask for a chemical compatibility table before choosing — guessing on media resistance is the most common cause of premature seal failure.
3. Cost & compliance — the final filter
Material cost runs roughly NBR < EPDM < silicone, but unit price is a small part of total cost. Silicone’s longer life in heat and its food/medical compliance often make it cheaper per year of service. For volume production, molding method matters too: LSR injection suits high-volume precision parts, while compression molding keeps tooling and MOQ low — at NEWTOP CUSTOM SILICONE we run both liquid and solid silicone lines, so the process is chosen after the material, not before.
Silicone vs EPDM vs NBR: Decision Tree
A practical way to reach the right answer in four questions:
- Does the seal contact petroleum oils or fuels?
- Yes → NBR (temperature below ~120 °C) or FKM (higher temperature or harsher chemicals). If the part also faces ozone/UV, NBR is a poor fit — switch to FKM or use a protective design.
- No → go to 2.
- Does the application see food, medical use, or sustained heat above 150 °C?
- Yes → Silicone.
- No → go to 3.
- Will the part live outdoors, in ozone/UV, steam, or water long-term?
- Yes → EPDM.
- No → go to 4.
- Is this a general-purpose indoor seal at moderate temperature?
- Yes → EPDM (best cost/performance balance) unless oil is present, in which case NBR.
This four-question tree covers roughly 90% of sealing decisions. Edge cases (vacuum, high-pressure, aggressive chemicals, FDA + high heat combined) are worth a conversation with a materials engineer — that is the point where a custom manufacturer earns its keep.
Application Scenarios
Automotive under-hood — engine bay seals see 120–150 °C plus oil mist: silicone for high-heat covers and boots, NBR for fuel-system O-rings, EPDM for weatherstripping and door seals. All three materials coexist in one vehicle; the application decides.
Food processing — gaskets, tubing and O-rings contact food, cleaning chemicals and steam (CIP/SIP): silicone is the default for food-contact surfaces; EPDM is acceptable for water-side gaskets where food contact is indirect. Both can be specified with FDA-compliant grades.
Electronics & outdoor enclosures — gaskets for LED housings, junction boxes and solar connectors need ozone/UV resistance: EPDM and silicone both work; silicone adds a wider temperature window and better long-term sealing force.
Medical devices — biocompatibility (USP Class VI / ISO 10993) and precision drive the choice to silicone, often LSR for complex geometries. NBR and EPDM are rarely specified for implantable or long-term skin-contact parts.
HVAC & water systems — EPDM dominates: water, steam, ozone and cost all favor it. NBR appears only where oil is present in the system.
Common Selection Mistakes
- Choosing by cost first — the cheapest material that survives the media and temperature is the right one; the cheapest material overall is not.
- Ignoring ozone/UV for outdoor parts — NBR outdoors cracks within a year or two; EPDM or silicone is required.
- Confusing peak and continuous temperature — a datasheet’s peak number is not a continuous-service license.
- Assuming “food grade” means the same thing everywhere — FDA, LFGB, EU 1935/2004 and USP Class VI are different scopes; verify against your target market.
- Forgetting compression set — a seal that hardens and loses squeeze force leaks long before it visibly fails. Ask for compression set data (ASTM D395) at your actual service temperature, not at room temperature.
- Specifying material before process — material and molding method interact (LSR vs solid silicone tooling, tolerances, MOQ). Confirm both together with the manufacturer.
How to Verify Material Performance Before You Source
When a supplier hands you a material recommendation, verify it:
- Datasheet numbers — hardness (Shore A), tensile strength (ASTM D412), elongation, compression set (ASTM D395), temperature range, and the test conditions behind each number.
- Certification scope — FDA 21 CFR 177.2600, LFGB, USP Class VI and UL are different claims; confirm which one applies to your product and market.
- Real part, not just raw material — molded and cured parts can behave differently from the raw compound; ask for test data on finished parts.
- Consistency across batches — for volume production, request batch traceability and lot-to-lot variation data.
FAQ
Q: Which is better — silicone or EPDM for outdoor gaskets?
A: Both resist ozone and UV well. EPDM is usually the cost-effective choice for outdoor weathering; silicone adds a wider temperature range and better long-term sealing force but costs more. Choose EPDM for standard outdoor service, silicone for extremes or food/medical contact.
Q: Is NBR or silicone better for oil seals?
A: NBR — silicone has poor resistance to petroleum oils. Use NBR for oil contact up to ~120 °C; switch to FKM (Viton-type) for higher temperatures or aggressive oils.
Q: Can EPDM be used for food contact?
A: Food-grade EPDM exists and is used for water-side and indirect food-contact gaskets. For direct food contact, silicone is the more common and more broadly certified choice (FDA 21 CFR 177.2600, LFGB).
Q: What temperature can silicone seals withstand?
A: Typical continuous service is about −60 to 230 °C, with special grades extending beyond. Short peaks can go higher, but repeated peaks accelerate aging.
Q: What is the cheapest sealing material of the three?
A: NBR is generally the lowest-cost, followed by EPDM, with silicone the most expensive per kilogram. Compare total cost — lifespan, failure risk and compliance — not just material price.
Q: What does compression set mean for seals?
A: Compression set measures how much a rubber loses its ability to spring back after being compressed at temperature. Low compression set means the seal keeps its squeeze force longer. Silicone, especially platinum-cured, typically shows excellent compression set.
Conclusion
There is no “best” sealing material — only the right one for the temperature, the media and the budget. Silicone for heat, food/medical and precision; EPDM for outdoor, steam and water at low cost; NBR for oils and fuels under moderate temperatures. When the application is unusual, verify with datasheet numbers, finished-part testing and a manufacturer that runs the process — not just the material.
If you are specifying a custom silicone part — a gasket, O-ring, boot, tube or precision component — talk to engineers who mold both liquid and solid silicone in-house. NEWTOP CUSTOM SILICONE is a 15-year custom silicone parts manufacturer with an in-house CNC tooling center, dual LSR and solid-silicone production lines, and capacity from single prototypes to 10k+ volume orders, with quotes delivered within 24–48 hours.
