Glass fiber

Glass fiber is made up of many very thin strands of glass. While glassmakers have tried creating such fibers for centuries, large-scale production only became practical after advances in precision machine tools. In 1893, Edward Drummond Libbey displayed a dress at the World's Columbian Exposition that used glass fibers as fine and textured as silk. Glass fibers can also form naturally, as seen in Pele's hair.

One common form of glass fiber is glass wool, a type of thermal building insulation invented by Games Slayter of Owens-Illinois between 1932 and 1933. This product, sold under the trade name Fiberglass (now a genericized trademark), is made by bonding fibers to trap many small air pockets, creating a low-density material. As a reinforcement, glass fiber offers mechanical properties similar to those of polymer or carbon fiber. It is less rigid than carbon fiber but much cheaper and less brittle in composites. These reinforced composites are used in marine and piping industries due to their environmental resistance, impact tolerance, and high strength-to-weight ratio.

**Fiber formation** Glass fiber is produced by extruding thin strands of silica-based or other glass formulations into fine fibers suitable for textiles. The technique of heating and drawing glass into fibers has been known for millennia, practiced in ancient Egypt and Venice. Before modern textile applications, all glass fiber was made as staple—clusters of short lengths.

The modern method for making glass wool was invented by Games Slayter at Owens-Illinois Glass Company in Toledo, Ohio. He filed a patent for the process in 1933, and the first commercial glass fiber production began in 1936. In 1938, Owens-Illinois and Corning Glass Works formed Owens-Corning Fiberglas Corporation, which introduced continuous filament glass fibers and remains a major producer today.

The most common glass fiber type is E-glass, an alumino-borosilicate glass with less than 1% alkali oxides, used mainly in glass-reinforced plastics. Other types include A-glass (alkali-lime glass with little or no boron oxide), E-CR-glass (alumino-lime silicate with high acid resistance), C-glass (alkali-lime glass with high boron oxide for insulation), D-glass (borosilicate glass with low dielectric constant), R-glass (alumino silicate without MgO or CaO, for high mechanical requirements), and S-glass (alumino silicate with high MgO for high tensile strength).

Pure silica, when cooled as fused quartz into a glass with no true melting point, can be used as fiber but requires very high working temperatures. To lower this temperature, fluxing agents are added. Ordinary A-glass (soda lime glass, often from crushed cullet) was the first type used. E-glass, alkali-free and originally for electrical applications, was the first continuous filament formulation and now accounts for most global fiberglass production, also being the largest consumer of boron minerals. However, it is vulnerable to chloride attack and unsuitable for marine use. S-glass (for strength) is used where high tensile modulus is critical, such as in aircraft and building composites; it is known as R-glass in Europe. C-glass (for chemical resistance) and T-glass (a North American variant) resist chemical attack and are common in insulation-grade blown fiberglass.

**Chemistry** Textile-grade glass fibers are based on silica (SiO₂). In pure form, silica exists as a polymer, (SiO₂)n, with no true melting point. It softens up to 1200°C, where degradation begins, and at 1713°C most molecules move freely. If extruded and cooled quickly at this temperature, the glass cannot form an ordered structure. The polymer consists of SiO₄ groups arranged as tetrahedra with a silicon atom at the center and four oxygen atoms at the corners, bonded into a network by shared oxygen atoms.

The vitreous and crystalline states of silica (glass and quartz) have similar molecular energy levels, meaning the glassy form is extremely stable. To induce crystallization, it must be heated above 1200°C for long periods. Although pure silica is viable, its high working temperature is a drawback unless specific chemical properties are needed. Impurities are therefore added to lower the working temperature and impart other beneficial properties. The first glass used for fiber was soda lime glass.