Glass fibres. Coloured scanning electron micrograph (SEM) of glass fibres (rod shapes). Glass fibres are often used as a reinforcing agent. They are woven into sheets and then impregnated with a plastic resin. When dry the finished material is known as glass fibre reinforced plastic (GRP), or simply fibreglass. GRP is thermosetting (malleable before curing to a stronger form through the addition of energy) and most often uses either polyester or vinylester. Glass fibre materials are hard, strong and light, and are used in the construction of aircraft, cars and yachts. Magnification: x2200 when printed 10 centimetres wide.