Glass-Reinforced Plastic

Glass-reinforced plastic (GRP) is a composite material or fiber-reinforced plastic made of a plastic reinforced by fine glass fibers. Like graphite-reinforced plastic, the composite material is commonly referred to by the name of its reinforcing fibers (fiberglass). Thermosetting plastics are normally used for GRP production—most often unsaturated polyester, but vinylester or epoxy are also used. Traditionally, styrene monomer was used as a reactive diluent in the resin formulation giving the resin a characteristic odor. More recently alternatives have been developed. The glass can be in the form of a chopped strand mat (CSM) or a woven fabric.

As with many other composite materials, the two materials act together, each overcoming the deficits of the other. Whereas the plastic resins are strong in compressive loading and relatively weak in tensile strength, the glass fibers are very strong in tension but have no strength against compression. By combining the two materials, GRP becomes a material that resists both compressive and tensile forces well. The two materials may be used uniformly or the glass may be specifically placed in those portions of the structure that will experience tensile loads.