Silicone rubber contains methyl and vinyl groups attached to the main silicone chain. Silicone O-rings are characterised by excellent resistance to temperature extremes and thermal cycling. Silicone does not impart odour or taste, which makes it suitable for many food and pharmaceutical applications. Silicone rubber however, has poor mechanical properties as compared to other elastomers and for this reason silicone O-rings are generally not used in dynamic applications. It is not suitable for use with silicone O-ring lubrication, PTFE alternatives should be used instead.