Borosilicate glass is a type of glass with the main glass-forming constituents silica and boron oxide. In addition to the quartz, sodium carbonate, and calcium carbonate traditionally used in glass making, boron is used in the manufacture of borosilicate glass. Typically, the resulting glass composition is about 70% silica, 10% boron oxide, 8% sodium oxide, 8% potassium oxide, and 1% calcium oxide (lime).
Borosilicate glasses are most well known for having very low coefficient of thermal expansion, about one-third that of ordinary glass. making them resistant to thermal shock, more so than any other common glass. This reduces material stresses caused by temperature gradients, thus making it more resistant to breaking.