Improved glass compositions for glass fibers typically useful for fire resistant blankets or containers to provide high burn-through resistance at temperatures of 2,300 F. and typically comprising 10.23% to 81.81% silica, 2.0% to 26.00% alumina, 3.0% to 15.0% calcium oxide, 0% to 10.50% magnesium oxide, 1.0% to 18.0% ferrous+ferric oxide, and 0% to 4.0% titanium dioxide; the improved glass compositions may include 0% to 9% lithium oxide, 0% to 9% boron oxide, 0% to 6.0% manganese oxide, and 0% to 4.0% phosphorous oxide.