SMC/Fiberglass Filler: Reinforcing Fibers USC Garage Pouches are your premier single-use solution in the body repair and refinish category, used by DIY’ers and pros alike. From dents and small repairs on aluminum, steel and fiberglass to repairs around the home on wood, metal and plastics. USC Garage SMC/Fiberglass Filler is a waterproof filler, structurally rated to repair sheet molding compound and works on fiberglass. It’s also easier to sand than conventional fiberglass fillers