Chopped strand fiberglass mat (or CSM) is a type of reinforcement used in fiberglass composites. It is made up of glass fibers that have been laid randomly across one another and then held together by binding agent.
CSM is typically used in the hand lay-up technique for mold making and composite reinforcement. Sheets of this non-woven Fiberglass mat are placed into a mold and then saturated with a resin. This resin is typically a vinylester or polyester based resin system. Because the binding agent dissolves into the resin, the material then easily conforms into different shapes once it has been fully wetted out.