Smooth-On Rebound 25 Silicone Rubber is a self-thickening, platinum-cure silcone for making brush-on molds. Apply with a brush or spatula — holds on a vertical surface without sagging. Quick cures to a soft, flexible rubber with negligible shrinkage. Four thin layers yield a stretchy, strong, and durable mold for casting wax, gypsum, concrete, low-temperature melt metal alloys, or resins. It has a 1:1 mix ratio by volume. For best results, use Smooth-On Plasti-Paste as a support shell. Smooth-On Rebound 25 Silicone Rubber comes in a package of two 16 oz (473 ml) jars. Warning — Not for use in making molds of models containing sulfur, e.g., sulfur-bearing clays.