Glass-reinforced Plastic (GRP) (GRP)

A fibre-reinforced composite in which glass reinforcement is embedded in a cured polymer resin.

The reinforcement may be chopped strand mat, woven cloth, stitched fabric or unidirectional fibres, while the matrix is commonly polyester, vinyl ester or epoxy resin. Strength and stiffness depend on fibre type, orientation and quantity, laminate design, resin choice and the quality of consolidation and cure.

GRP does not rust like steel or rot like untreated timber, but it can suffer impact cracking, fatigue, delamination, water ingress, osmosis and ultraviolet degradation of exposed resin. Inspection and repair must consider the load paths and any core material, not merely restore the visible surface.