Glass

Glass fiber has roughly comparable mechanical properties to other fibers such as polymers and carbon fibre. Although not as strong or as rigid as carbon fiber, it is much cheaper and significantly less brittle when used in composites. Glass fibers are therefore used as a reinforcing material for many polymer products; to form a very strong and relatively lightweight fibre-reinforced (FRP) composite material called glass-reinforced plastic (GRP), also popularly known as "fiberglass". This structural material product contains little or no air or gas, is more dense, and is a much poorer thermal insulator than is glass wool.