GRP, Glass Reinforced Plastic

Glass reinforced plastic, also called fiberglass or GRP, is the standard hull material for production yachts: glass fiber laid up in a polyester or vinylester resin matrix, usually over a cored sandwich of balsa or foam for stiffness without weight. It allowed builders such as Beneteau and Jeanneau to mold identical hulls cheaply from a single tool, which is what made one-design fleets and the mass leisure market possible from the 1960s. Osmotic blistering of the gelcoat is its characteristic long-term failure.