In addition to the silicone polymer

In addition to the silicone polymers
described above, the majority of silicone elastomers incorporate
“filler.” Besides acting as a material extender, as the
name implies, filler acts to reinforce the cross-linked matrix.
The strength of silicone polymers without filler is generally
unsatisfactory for most applications (Noll, 1968). Like most
other noncrystallizing synthetic elastomers, the addition of
reinforcing fillers reduces silicone’s stickiness, increases its
hardness and enhances its mechanical strength. Fillers might
also be employed to affect other properties; for example, carbon
black is added for electrical conductivity, titanium dioxide
improves the dielectric constant, and barium sulfate increases
radiopacity. These and other materials are used to pigment the