Fiberglass (also called glass-reinforced plastic, GRP, glass fiber-reinforced plastic, or GFRP), is a fiber reinforced polymer made of a plastic matrix reinforced by fine fibers of glass. It is also known as GFK (for Glasfaserverstärkter Kunststoff).

Fiberglass is a lightweight, extremely strong, and robust material. Although strength properties are somewhat lower than carbon fiber and it is less stiff, the material is typically far less brittle, and the raw materials are much less expensive. Its bulk strength and weight properties are also very favorable when compared to metals, and it can be easily formed using molding processes.

The plastic matrix may be epoxy, a thermosetting plastic (most often polyester or vinylester) or thermoplastic.

Common uses of fiber glass include boats, automobiles, baths, hot tubs, water tanks, roofing, pipes, cladding and external door skins.

Fiber

Unlike for example, glass fibers used for insulation, for the final structure to be strong, the fiber's surfaces must be almost entirely free of defects, as this permits the fibers to reach Gigapascal tensile strengths. If a bulk piece of glass were to be defect free, then it would be equally as strong as glass fibers; however it's generally impractical to produce and maintain bulk material in a defect free state, although it can be done under laboratory conditions.

Production

The manufacturing process for glass fibers suitable for reinforcement uses large furnaces to gradually melt the sand/chemical mix to liquid form, then it is extruded through bundles of very small orifices (typically 17-25 micrometres in diameter for E-Glass, 9 micrometres for S-Glass). These filaments are then sized with a chemical solution. The individual filaments are now bundled together in large numbers to provide a roving. The diameter of the filaments, as well as the number of filaments in the roving determine its weight. This is typically expressed in yield-yards per pound (how many yards of fiber in one pound of material, thus a smaller number means a heavier roving, example of standard yields are 225yield, 450yield, 675yield) or in tex-grams per km (how many grams 1 km of roving weighs, this is inverted from yield, thus a smaller number means a lighter roving, examples of standard tex are 750tex, 1100tex, 2200tex).

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

Sizing

A sort of coating, or primer, is used which both helps protect the glass filaments for processing/manipulation as well as ensure proper bonding to the resin matrix, thus allowing for transfer of shear loads from the glass fibers to the thermoset plastic, without this bonding, the fibers can 'slip' in the matrix and localised failure would ensue.

Properties

An individual structural glass fiber is both stiff and strong in tension and compression—that is, along its axis. Although it might be assumed that the fiber is weak in compression, it is actually only the long aspect ratio of the fiber which makes it seem so; i.e., because a typical fiber is long and narrow, it buckles easily. On the other hand, the glass fiber is unstiff and unstrong in shear—that is, across its axis. Therefore if a collection of fibers can be arranged permanently in a preferred direction within a material, and if the fibers can be prevented from buckling in compression, then that material will become preferentially strong in that direction.

Furthermore, by laying multiple layers of fiber on top of one another, with each layer oriented in various preferred directions, the stiffness and strength properties of the overall material can be controlled in an efficient manner. In the case of fiberglass, it is the plastic matrix which permanently constrains the structural glass fibers to directions chosen by the designer. With chopped strand mat, this directionality is essentially an entire two dimensional plane; with woven fabrics or unidirectional layers, directionality of stiffness and strength can be more precisely controlled within the plane.

A fiberglass component is typically of a thin "shell" construction, sometimes filled on the inside with structural foam, as in the case of surfboards. The component may be of nearly arbitrary shape, limited only by the complexity and tolerances of the mold used for manufacturing the shell.

Applications

Fiberglass is an immensely versatile material which combines its light weight with an inherent strength to provide a weather resistant finish, with a variety of surface textures.

Fiberglass was developed in the UK during the Second World War as a replacement for the molded plywood used in aircraft radomes (fiberglass being transparent to microwaves). Its first main civilian application was for building of boats, where it gained acceptance in the 1950s. Its use has broadened to the automotive and sport equipment sectors as well as model aircraft, although its use there is now partly being taken over by carbon fiber which weighs less per given volume and is stronger both by volume and by weight. Fiberglass uses also include hot tubs, pipes for drinking water and sewers, office plant display containers and flat roof systems.

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

Fiberglass is also used in the telecommunications industry for shrouding the visual appearance of antennas, due to its RF permeability and low signal attenuation properties. It may also be used to shroud the visual appearance of other equipment where no signal permeability is required, such as equipment cabinets and steel support structures, due to the ease with which it can be molded, manufactured and painted to custom designs, to blend in with existing structures or brickwork. Other uses include sheet form made electrical insulators and other structural components commonly found in the power industries