Glass fibres are well-known reinforcing agents for different kinds of materials. For example, plastics, polyesters and epoxy resins can be reinforced using glass fibres originally developed for electrical applications; the resistance of bituminous materials is increased with the addition of chemically resistant glass fibres, and alkali resistant fibres are used in reinforced concrete. The price of conventional glass fibres is high because of the cost of the raw materials and of the high energy cost involved in the melting process. Therefore, a process which would allow the substitution of the natural raw materials with secondary products such as certain inorganic industrial wastes which have a lower melting temperature, would be of interest because it could increase the saving of energy and natural resources. Moreover, the disposal of industrial wastes in landfill would be reduced.