Some glasses do not break when heated. How?
Answers
Glass (drinkware) is made up of glass (material) with a certain amount of thickness. When you pour hot water into a glass (which is at room temperature), the inner layer of the glass will absorb heat. When a material absorbs heat, it expands. Glass is no exception to that. (i.e. The inner layer of the glass will expand.) Since glass is not a good conductor of heat, the conduction of heat through the glass layer is slow. Hence, the inner layer of the glass is hot while the outer layer is still relatively cold.
This temperature difference will cause the inner layer of the glass to expand significantly more than the outer layer. This difference in the amount of expansion exerts a tremendous amount of pressure on the outer layer. If the glass is unable to hold up against the large pressure, the glass will crack. The magnitude of the temperature difference between the inner and outer layers will determine the likelihood of the glass cracking. If the water is really hot, the glass will definitely crack.
Glass is less likely to break or shatter if we warm it up gradually. ... This effect of thermal shock is strong enough that it even can cause special types of glass like Pyrex or borosilicate glass, used in a lot of commercial labware, to shatter.