What is GRP?

Glass Reinforced Plastic (GRP)

Fiberglass Recycling

GRP stands for Glass Reinforced Plastic (or Polymer). You may also know it as FRP (Fibre Reinforced Plastic) or even as Fibreglass. It is a matrix of recycled plastic and recycled glass with a tough waterproof resin to bond it all together.


Fibreglass or fibreglass is a common type of fibre-reinforced plastic using glass fibre. The fibres may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass cloth.

More affordable and more flexible than carbon fibre, it's stronger than many metals by weight; it's non-magnetic, non-conductive, transparent to electromagnetic radiation, can be molded into complicated shapes, and is chemically inert under many circumstances. Applications comprise of aircraft, boats, cars, bathtubs and enclosures, swimming pools, hot tubs, septic tanks, water tanks, roofing, pipes, cladding, surfboards, and external door skins.

Unlike glass fibres used for insulation, for the final structure to be strong, the fibre's surfaces must be almost entirely free of defects, as this permits the fibres to reach gigapascal tensile strengths.


The process of manufacturing fibreglass is called pultrusion. The manufacturing process for glass fibres suitable for reinforcement uses large furnaces to gradually melt the silica sand, limestone, kaolin clay, fluorspar, colemanite, dolomite and other minerals until a liquid forms. It is then extruded through bushings (spinneret), which are bundles of very small orifices (typically 5–25 micrometres in diameter for E-Glass, 9 micrometres for S-Glass).

These filaments are then sized (coated) with a chemical solution. The individual filaments are now bundled in large numbers to provide a roving. The diameter of the filaments, and the number of filaments in the roving, determine its weight, typically expressed in one of two measurement systems:

Yield, or yards per pound (the number of yards of fibre in one pound of material; thus a smaller number means a heavier roving). Examples of standard yields are 225yield, 450yield, 675yield.

Tex, or grams per km (how many grams 1 km of roving weighs, inverted from yield; thus a smaller number means a lighter roving). Examples of standard tex are 750tex, 1100tex, 2200tex.

GRP Trailor

These rovings are then either used directly in a composite application such as pultrusion, filament winding (pipe), gun roving (where an automated gun chops the glass into short lengths and drops it into a jet of resin, projected onto the surface of a mold), or in an intermediary step, to manufacture fabrics such as chopped strand mat (CSM) (made of randomly oriented small cut lengths of fibre all bonded together), woven fabrics, knit fabrics or unidirectional fabrics.


Fibreglass is an immensely versatile material due to its lightweight, inherent strength, weather-resistant finish and variety of surface textures.

The development of fibre-reinforced plastic for commercial use was extensively researched in the 1930s. It was of particular interest to the aviation industry. During World War II, fibreglass was developed as a replacement for the molded plywood used in aircraft.

Its first main civilian application was for the building of boats and sports car bodies, where it gained acceptance in the 1950s. Its use has broadened to the automotive and sports equipment sectors. In the production of some products, such as aircraft, carbon fibre is now used instead of fibreglass, which is stronger by volume and weight.

Advanced manufacturing techniques such as pre-pregs and fibre rovings extend fibreglass's applications and the tensile strength possible with fibre-reinforced plastics.

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