Borosilicate glass

Borosilicate glass is glass that contains boron oxide as well as silica. The boron oxide lets it withstand sudden changes in temperature without cracking. Malay: kaca borosilikat · Chinese: 硼硅玻璃.

The special property comes from how little the glass expands when heated. Ordinary soda-lime glass expands quite a lot on heating, so a rapid change in temperature makes different parts of the glass expand or contract by different amounts and it cracks. Adding boron oxide greatly reduces this expansion, so borosilicate glass can be heated strongly and then cooled quickly without breaking. That heat resistance, together with good chemical resistance, is exactly what is needed where glass must be heated over a flame or filled with hot liquid.

Example. Borosilicate glass is used for laboratory apparatus such as beakers, boiling tubes and conical flasks that are heated during experiments, and for ovenware and cookware that go from a hot oven to a cool surface. In each case it survives temperature changes that would shatter soda-lime glass.

Confusion to avoid. Do not confuse borosilicate glass with soda-lime glass. Both are mainly silica, but borosilicate glass has boron oxide added and resists sudden heating and cooling, while soda-lime glass is cheaper but cracks under the same treatment.

To answer well, connect the property to the use at every step: boron oxide gives a low thermal expansion, a low thermal expansion means the glass survives sudden temperature change, and that is why laboratory glassware and ovenware are made from it. Skipping the middle step, and simply stating that borosilicate glass is “better”, is where many answers lose their mark.

The soda-lime versus borosilicate comparison, and the reason boron oxide is added, is a predictable materials question in SPM Chemistry.