Whilst we would not choose to use either silicon or PVC as an insulation material, both are excellent choices for damping unwanted vibrations. We use a soft PVC for outer jackets but surround it with a harder outer casing for added protection.

http://www.techlib.com/reference/insulation.html

http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/skineffect/page1.html