Silicone

Silicone - or Polyorganosiloxane - is a polymer that is not to be confused with the chemical element silicon which forms part of silicone together with organic compounds. Thanks to this combination of organic and inorganic compounds, silicone is quite unique in terms of its range of properties.
 

So it is that silicone is hydrophob, thermostable, and generally to be considered biocompatible. It is thus not only a popular material for moulding and craftsmanship of all sorts but also for medical applications.