Glass fibre is a fine, fibrous material made from the same type of raw materials used to produce flat glass.  A wide range of grades is manufactured, which can be divided into reinforcing, insulation and optical categories.  Glass fibre is characterised by high tensile and impact strength, lightweight, high resistance to chemical attack and generally low cost.  These properties make glass fibre suitable for a very wide range of reinforcement applications in plastics and composites.  Materials reinforced with glass fibre are used in interior and exterior residential, commercial, industrial and agricultural structures, as well as in transport and consumer applications.  Glass fibre fabrics are widely used as construction materials because of their resistance to fire.

Kaolin is only used in the manufacture of reinforcing glass fibre, also known as continuous filament glass fibre or textile grade.  In this type of glass fibre, kaolin makes up to around 29% of the weight of the batch formulation in some cases.  Other typical constituents of textile grade glass fibre are silica sand (29%), limestone (30%) and boron compounds (12%).  This type of glass fibre is used to increase the strength of plastics, rubber cement and other materials.  

One of the most important applications of textile grade glass fibre is in reinforced plastics, especially in reinforced thermosetting polyester resins.  Since the 1950s, glass fibre has steadily taken over from wood in the construction of the hulls of boats and ships.  In the motor industry, glass fibre has been used for a similar length of time, initially to replace body panels and similar large structural components.  In recent years, new products reinforced with glass fibre have been developed for components, such as clutches in automobiles.

Various grades of glass can be used to produce textile grade glass fibre.  The standard textile grade glass fibre is E-glass available as chopped fibres, mats, rovings and woven products.  E-glass fibre is the mostly commonly produced form of glass fibre but is susceptible to attack by dilute mineral acids making it unsuitable for some applications.  As a result, C-glass fibre is used in composites that are likely to come into contact with acids with a further use in reinforcing bituminous roofing sheets.  S-glass fibre is specialised glass fibre used in applications where a high strength is required.  This form of glass is considerably more expensive than the other types used in glass fibre.  

Insulation grade glass fibre (IGFG), also known as insulating glass fibre or glass wool, is mainly used to insulate buildings.  Insulation and textile grade glass fibre are the most important types in terms of the quantity produced.  

Optical grade glass fibre is manufactured in much lower quantities, but is far more valuable than the other two main forms of glass fibre.  Production of optical fibres is growing as demand for fibre optic cables for use in telecommunications is increasing.

Other types of glass fibre include D, M, L and AR-glass fibre.  D-glass fibre is mainly used in the electronics sector in applications such as printed circuit boards because of its high electrical resistance.  AR-glass fibre was developed for use as a reinforcement material for cement.  This type of glass fibre has good resistance to alkalis, good durability and is also much lighter than traditional cement.  The main application is as a replacement for asbestos in construction products such as roofing.  M-glass fibre is highly elastic and L-glass fibre is resistant to radiation making them useful in specialised applications.