What is Boroslicate glass? boroslicate Boroslicate glass is a type of glass that contains boron trioxide which allows for a very low coefficient of thermal expansion...... Boroslicate glass is a type of glass that contains boron trioxide which allows for a very low coefficient of thermal expansion. This means it will not crack under extreme temperature changes like regular glass. Its durability has made it the glass of choice for high-end restaurants, laboratories and wineries. What most people don’t realise is that not all glass is created equally. Borosilicate glass is made up of about 15% boron trioxide, which is that magical ingredient that completely changes the behaviour of glass and makes it thermal shock resistant. This allows the glass to resist extreme changes in temperature and is measured by the “Coefficient of Thermal Expansion”, the rate at which the glass expands when it is exposed to heat. Thanks to this, borosilicate glass has the ability to go straight from a freezer to an oven rack, without cracking.