Klean Klay is the perfect product to form masters. Unlike some clays, Klean Klay will not inhibit the curing of mold materials. It's non-hardening and it can be used over and over again.
Klean Klay is also a great material for filling in seams around the base of mold boxes. It forms a tight joint to prevent mold materials from linking. When the mold is cured simply peel away the Klean Klay and reuse it in your next project.
Klean Klay is non-toxic and safe for use by children. Klean Klay comes in 450g packages.