The first mold made from the maquette should be flexible so it can be
peeled away from the irregular shape of the clay model. It should be durable so that it can be used many times. And it must be able to withstand the
heat of the liquid wax.
Silicone rubber fits these requirements perfectly. It is a synthetic elastic polymer, or "elastomer" that contains silica particles that
give it strength, rigidity, and heat resistance.
Liquid silicone rubber is mixed from two parts and hardens fairly quickly after it is mixed. Once hard, it does not react with other chemicals,
and is widely used in medical devices, household utensils, and industry.
Silicone rubber also does not shrink when it dries, so it keeps the original shape of the clay maquette perfectly.
Before silicone rubber was avaiable, natural latex was used, but it is not as stable and dries much more slowly.