I believe I have mentioned Rose Brand’s molding cloth before (if not check it out here: http://www.rosebrand.com/subcategory22/molding-cloth.aspx). I just came across 2 more products that are very similar:
Foss Shape (http://www.dazian.com/html/fosshape.html)
Both of these materials require heat to activate, with the Foss Shape material requiring a higher temperature. These materials are recommended for “headpieces, sub-structures, ornamental effects, masks, props and scenic materials.” The materials cut easily, and will bond to itself as well as other materials, and can be sewn.