Silastic HS II RTV Silicone Rubber is one of Dow Corning's medium viscosity two-part silicone rubbers. It has a viscosity of 45,000 cps with a Shore A hardness of 20 and a tear strength of 120. The main difference in this Silastic from the others is its high strength and long mold life, which allows more reproductions per mold. It easily fills tiny crevices and indentations and is very easy to work with and pour. It offers a wide choice of handling and cured physical properties. Vacuum deairing is required. It is especially good for patterns with unusual configurations, severe undercuts and close tolerances. There is no inhibition sensitivity to modeling clays and most adhesives which could cause incomplete cure of mold. It does have moderate dimensional shrinkage.