Smooth-On has been making moldmaking materials since 1895. Their headquarters is in Easton, PA. They have a number of lines of products which are great for craft work. In particular, they make liquid rubber and liquid plastics which can be used for making molds and casts. Many art, craft, and plastics stores (like Pearl) carry parts of their product line. In addition to model, prototype, and sculpture making, their products are also useful for taxidermy, cold casting, and decorative concrete casting.

Some of their products include:

If you're looking to get started with making molds and casts for craft projects, Smooth-Sil 901 for making molds and Smooth-Cast 300 for casting are easy to use and cure quickly.

For more details about their products, see their website at: