Fiberglass mat (also known as chopped strand mat) has strands of fiber that are randomly oriented and held together with a styrene binder. When a resin is added to the mat, the binder dissolves and the fibers can be moved around. Mat is used to build up thickness quickly and is often layered in between fiberglass fabric. It is compatible with polyester and vinyl ester resin. It is NOT compatible with epoxy resin. A full roll is approximately 120 lbs.