Silicone is a semi-organic elastomer with outstanding resistance to extremes of temperature with corresponding resistance to compression set and retention of flexibility. 
Silicone elastomers provide excellent resistance to ozone, oxygen, and moisture. 

Low physical strength and abrasion resistance combined with high friction properties limit silicone to static seal applications. 
Silicone utilizes a flexible siloxane backbone rather than a carbon backbone like many other elastomers and has very low glass transition temperatures.