One of the most common questions from outdoor-product designers is "how long will silicone last in the sun?" The short answer: silicone is among the most UV- and weather-resistant elastomers available — but "resistant" is not "immune." Here is what actually happens, and how to specify correctly.
Why Silicone Weathers So Well
Silicone's backbone is a silicon–oxygen (Si–O) bond, which is fundamentally stronger and more stable than the carbon–carbon (C–C) backbone of organic elastomers like EPDM, NBR or natural rubber. UV photons carry enough energy to break C–C bonds and trigger the oxidation and chain scission that cause cracking and chalkiness in most rubbers — but the Si–O bond resists this photodegradation far better. That single structural difference is why silicone seals, gaskets and housings routinely outlast their organic-rubber counterparts outdoors and under sunlight.
How Silicone Compares to Other Elastomers Outdoors
| Material | UV / sunlight | Ozone | Typical outdoor behavior |
|---|---|---|---|
| Silicone (VMQ) | Excellent | Excellent | Slow, minor surface changes; minimal cracking over years |
| EPDM | Good | Excellent | Good outdoors but can chalk and discolor over long exposure |
| NBR (nitrile) | Poor | Poor | Cracks and hardens relatively quickly outdoors |
| Natural rubber | Poor | Poor | Rapid ozone cracking unless heavily protected |
| Fluorosilicone (FVMQ) | Very good | Excellent | Adds fuel/oil resistance to silicone's weather resistance |
What Actually Changes — Yellowing and Hardness
Even silicone is not completely static outdoors. The changes you should design for are:
- Yellowing / discoloration — transparent or light-colored silicone can yellow under prolonged UV, especially with certain cure systems or additives. For optical and clear parts this matters more than for pigmented parts.
- Surface chalking — a fine powdery surface layer can form over very long exposure, usually cosmetic rather than structural.
- Slight hardness drift — marginal stiffening or softening depending on the grade and filler system, generally far smaller than organic rubbers.
If color stability is critical, specify UV-stabilized or pigment-selected grades and confirm the cure system. Platinum-cured and additive-selected compounds typically offer the best color stability.
How Weathering Is Tested
- QUV / xenon-arc accelerated weathering (ASTM G154, ASTM G155) — simulates UV and moisture cycles in days to estimate years of exposure.
- Ozone resistance (ASTM D1149 / ISO 1431) — confirms resistance to ozone cracking.
- Color / ΔE measurement — quantifies yellowing before and after exposure.
- Physical-property retention — tensile and hardness measured before and after aging to show retention percentage.
Always ask for property-retention data, not just a pass/fail statement — the percentage of tensile strength or elongation retained after a defined exposure is what lets you compare grades honestly. See our testing methods page for the broader test suite.
Specifying Silicone for Outdoor Use
- Choose platinum-cured or additive-selected grades for best color and property stability.
- For clear or optical outdoor parts, prioritize UV-stabilized transparent grades and confirm ΔE targets.
- For fuel or chemical + weather exposure, consider FVMQ fluorosilicone.
- For high-temp outdoor (engine bays, solar), combine silicone's weather resistance with its wide -60°C to +200°C+ service range.
- Request accelerated-weathering data relevant to your geography (e.g. QUV or xenon) rather than assuming "silicone = forever."
How CYES SILICONE Helps
We compound and mold silicone across Shore A 20–80, including UV-stabilized, transparent and FVMQ grades, and can support weathering-validation programs with tensile/hardness retention, color measurement and accelerated-aging data before release. Tell us your exposure environment and lifetime target, and we will recommend the grade and the testing that proves it.