High borosilicate glass has a very low coefficient of thermal expansion, only about one third that of ordinary glass. This will reduce the effect caused by temperature gradient stress and thus have stronger fracture resistance. Its very small shape deviation makes it essential for telescopes, mirrors and the disposal of high-level nuclear waste. High borosilicate glass does not break easily even when the temperature changes abruptly. When broken, high borosilicate glass develops large cracks rather than being crushed into particles. High borosilicate glass also has low dispersion and relatively low refractive index.
The linear expansion coefficient of high borosilicate glass G3.3 is (3.3 x 0.1) ×10-6/K, which is a kind of glass with sodium oxide (Na2O), boron oxide (B2O3) and silicon dioxide (SIO2) as the basic components. The content of borosilicate in the glass was higher, respectively: boron (12.5~13.5) % and silicon (78~80) %.