Silicone has excellent resistance to weathering and UV, and is often found in outdoor applications such as door and window seals. In contrast, natural rubber weathers very quickly and is not suited to outdoor applications. If your application involves exposure to the elements, silicone is the better choice.
Silicone o-rings are widely sought after for their outstanding resistance properties to a wide range of chemicals, temperatures, and weather conditions. Specifically, silicone is known to feature: Extreme temperature resistance from -50°C to 240°C. Superior insulating properties.