Abstract: A glass fiber of quaternary composition including SiO2, Al2O3, CaO, and MgO, each present in an amount of at least 5 wt. %, and having less than 3.3 wt. % B2O3, and less than 2.0 wt. % fluorine, wherein: 22.0<MgO+CaO=<35.0 wt %, and 27.0<MgO+Al2O3=<44.0 wt %. all amounts being expressed in weight % with respect to the total weight of the composition. Also disclosed is a method of making composite materials reinforced with such fibers, and their use in applications such as windmill blades, pressure vessels, components in the automotive, machinery, aerospace applications, and such products produced therewith.

Abstract: A glass fibre of quaternary composition including SiO2, AI2O3, CaO, and MgO, each present in an amount of at least 5 wt. %, and having less than 3.3 wt. % B2O3, and less than 2.0 wt. % fluorine, characterized by: 22.0<MgO+CaO?35.0 wt %, and 27.0<MgO+AI2O3?44.0 wt %. all amounts being expressed in weight % with respect to the total weight of the composition. Also disclosed is a method of making composite materials reinforced with such fibres, and their use in applications such as windmill blades, pressure vessels, components in the automotive, machinery, aerospace applications and such products produced therewith.