What is the difference between high borosilicate glass and ordinary glass

High borosilicate glass (also known as hard glass) is made by utilizing the conductive properties of glass at high temperatures, melting the glass by heating it inside, and processing it through advanced production technology. The prominent feature of high borosilicate glass is its coefficient of linear thermal expansion of (3.3 ± 0.1) * 10-6/K, which is about one-third of that of ordinary glass. This characteristic reduces the influence of temperature gradient stress and thus has stronger fracture resistance for instance:

In daily life, when we pour hot water into a glass cup that has just been filled with cold water or ice water, or use a glass cup that has just been boiled with hot water to receive ice water, ordinary glass cups will immediately break due to temperature stress, but high borosilicate glass will not experience this situation

Due to its temperature resistance, high borosilicate glass produces objects with very small shape deviations, making it an essential material for telescopes and reflectors