Why is borosilicate glass resistant to heat?

Borosilicate glass is highly resistant to heat and thermal shock primarily because of its low coefficient of thermal expansion. When ordinary glass is subjected to sudden temperature changes, internal stresses often cause it to fracture; however, borosilicate glass expands and contracts significantly less than typical soda-lime-silica glass, making it much more durable under such conditions.123

This property is achieved by incorporating boric oxide (B₂O₃) into the glass composition, often replacing much of the sodium oxide used in standard glass formulas. In addition to its thermal resistance, the inclusion of boric oxide and small percentages of alumina enhances the chemical stability of the material. Because of these characteristics, borosilicate glass is widely utilized in applications requiring high durability and resistance to temperature fluctuations, such as laboratory chemical glassware and domestic cookware.123