Why do glassware crack when it is hot and cold?

 Why do glassware crack when it is hot and cold?

Once hot water is added to a glass container, does its temperature increase simultaneously and expand without stressing? Because glass is such a poor conductor of heat and has delicate materials within its pores, temperature differences between inside and outside the glassware cause inconsistent expansion rates - for instance when injecting cold water into a cold glass bottle it will expand within itself but the outer circumference has not kept pace, being squeezed by its interior glass content instead.

Select glassware that can withstand both hot and cold conditions. A vessel with a small expansion rate should be chosen; its thickness must also be modest, and its form should not be too sharply curved; for this reason, circular flasks are commonly used as heating flasks during chemical experiments.

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Beverage factory or winery or food factory when product is canned usually use high temperature cans; there is usually only a temperature difference of 42 degrees between cans and canned glass containers; food should be packed at 110 degrees before preheating to 68 degrees before packing in glass jar. This is considered safe temperature coefficient.