An R-glass composition including SiO2 in an amount from 59.0 to 64.5% by weight, Al2O3 in an amount from 14.5 to 20.5% by weight, CaO in an amount from 11.0 to 16.0% by weight, MgO in an amount from 5.5 to 11.5% by weight, Na2O in N an amount from 0.0 to 4.0% by weight, TiO2 in an amount from 0.0 to 2.0% by weight, Fe2O3 in an amount from 0.0 to 1.0% by weight, B2O3 in an amount from 0.0 to about 3.0% by weight, K2O, Fe2O3, ZrO2, and Fluorine, each of which is present in an amount from 0.0 to about 1.0% by weight, and SrO and ZnO, each of which is present in an amount from 0.0 to about 2.0% by weight. In exemplary embodiments, the glass composition does not contain lithium or boron.