Smooth-On - Smooth-Cast 300 Liquid Plastic Compound & Mold Star 15 Slow Molding Silicone Rubber (1 Pint A & 1 Pint B) Mold Star rubbers are easy to use platinum silicones which are mixed 1A:1B by volume Mold Star silicones feature relatively low viscosities and vacuum degassing is not required for most applications The pot life of Mold Star 15 SLOW is 50 minutes and cure time is 4 hours at room temperature