Borosilicate glass is a type of glass that includes at least 5% boric oxide. The boric oxide makes the glass resistant to extreme temperatures, and also improves its resistance to chemical corrosion. This glass is very popular in the manufacture of scientific instruments, and it was once widely used to make glass for kitchens as well. Today, soda-lime glass is the glass of choice for kitchenware, due to the fact that it is generally cheaper to produce.
Borosilicate glass can handle both extreme heat and cold, making it very popular for laboratory glassware and other scientific instruments. It also has a reduced rate of thermal expansion, which can make it useful for things like telescopes and other high precision lenses where the surface of the lens must be very even to get a clear image.