The 1600 series are tin (or condensation) cured silicone elastomers and are generally the best for those mold making applications where surface inhibition might be a problem. Easy to use in its ten to one ratio (by weight) these elastomers can be modified by the addition of Viscosil for those situations where one might need a brushable compound, and can also be accelerated by the addition of Rapid Set for those of you who might be in a hurry to make a mold. All of our silicone rubbers can be thinned with Silicone Fluid, and colored with Silicone Pigments.
SR-1610 is the softest (shore A:10), and is milky translucent with a clear catalyst.
SR-1618 has a Shore A hardness of 15 and is great for those molds where maximum flexibility is needed. Includes yellow catalyst.
SR-1621 is a relatively soft, (shore A:23) tough material and is what we consider to be our "flagship" silicone. Includes blue catalyst.
SR-1644 is a harder polymer (shore A 40) but is not as tough as the SR-1621 and is used where one might need a mold that need not be flexed as much, or more accurate "keying" of multiple part molds is necessary. Includes yellow catalyst.
The 1600 series silicones are best used with waxes, cements, polyurethanes and polyester resins. Not recommended for casting epoxy resins or metal alloys
*SR-1621 1 gallon unit includes 8 lb. of part A, and 13 oz of part B catalyst