Golden - Acrylic Medium - GAC-400 Polymer (Heat Set) - 8 oz - GOLDEN GAC-400 Specialty Acrylic Polymer is a liquid acrylic polymer emulsion which dries to a hard, stiff film. When applied over a fabric support, such as cotton, linen or silk, the GAC 400 will serve to dramatically stiffen the support. This allows the artist to transform a lightweight fabric into a free-standing form that will hold its shape.