Hi Dana,
afaik most engine mounts are still made from natural rubber (NR). It is a
good compromise between high elasticity over a wide range of temperature and
the most important physical property - the price.
Only in case of higher temperature (like for encapsulated engines) one has
to consider other elastomers as EPDM or Silicone.
What Al means is high damping elements, usually made from butyl rubber, but
it is not used normally for engine mounts. Controlled damping in engine
mounts is sometimes done by filling them with vicous liquids - hydromounts-.
HTH MaTTHIAS