Abstract: The invention relates to glass reinforcing yams, the composition of which comprises the following constituents, within the limits defined below, expressed in percentages by weight: SiO2 50-65% Al2O3 12-20% CaO 13-16% MgO ?6-12% B2O3 0-3% TiO2 0-3% Na2O + K2O <2% F2 0-1% Fe2O3 <1. These yarns are made of a glass offering an excellent compromise between its mechanical properties represented by the specific Young's modulus and its melting and fiberizing conditions.

Abstract: The present invention relates to a sizing composition for glass strands composed of a solution with a viscosity of less than or equal to 400 cP comprising less than 5% by weight of solvent and comprising at least one thermally polymerizable base system, the said base system comprising at least 60% by weight of components with a molecular mass of less than 750 and comprising at least 60 % by weight of a mixture: of component(s) exhibiting at least one epoxy reactive functional group, and of component(s) exhibiting at least one anhydride reactive functional group. The invention also relates to a process using this composition and to the strands obtained according to this process and coated with the said composition.