What is commonly known as "fiberglass" today, however, was invented in 1938 by Russell Games Slayter of Owens-Corning as a material to be used as insulation. It is marketed under the trade name Fiberglas, which has become a genericized trademark. A somewhat similar, but more expensive technology used for applications requiring very high strength and low weight is the use of carbon fiber.

The nature of glass

Main article: Physics of glass

Glass is typically viewed as an elastic solid in which no significant crystallization has occurred. Thus there is no long-range ordering or extended formation of any Bravais lattice. It follows that glass, even as a fiber, has little crystalline structure (see amorphous solid). The properties of the structure of glass in its softened stage are very much like its properties when spun into fiber. One definition of glass is "an inorganic substance in a condition which is continuous with, and analogous to the liquid state of that substance, but which, as a result of a reversible change in viscosity during cooling, has attained so high a degree of viscosity as to be, for all practical purposes, rigid."

Generally speaking, the atomic or molecular structure of glass exists in a metastable state with respect to its crystalline form. This essentially reflects their formation from a non-equilibrium supercooled liquid state. Fundamental principles of Gibbs free energy minimization dictate this thermodynamic driving force towards crystallinity, long-range symmetry and thermodynamic equilibrium.

Since the early theoretical and experimental investigations on polymorphism and the various states of aggregation which can be assumed by a given substance, the vitreous state of matter has been recognized as having the mechanical response of both solid and liquid, depending on the time and length scale under consideration. This explains the age-old quandary of whether to label it as solid or liquid.

Since the earliest work on glass, much work has been done to elucidate the primary microstructural features of glass forming substances over a wide range of spatial scales. As a result of this work, one emerging school of thought is that a glass is simply the limiting case of a polycrystalline solid. Within this framework, "domains" exhibiting various degress of short-range order become the building blocks of both metals and alloys, as well as glasses and ceramics. Distributed both between and within these domains are microstructural defects which will provide the most ideal locations for the occurence of inelastic, irreversible plastic flow and deformation.

Fiber formation