The Pyrex Glass Controversy That Just Won't Die

[localroger]

37. No, the whole point of borosilicate is no stress

Normal glass shatters because it is enormously stiff as well as strong, and when part of it expands a bit due to a hot spot while the rest doesn't, the resulting stress can shatter it. Borosilicate is formulated to simply not expand when it gets hotter. Hot spots don't cause stress. Other than that, though, it breaks about like any window pane.

Tempered glass is far stronger than normal glass because it is "prestressed" by internal forces pulling it together. It does expand when it gets hotter, but the additional stress isn't comparable to the stress that's already there pulling it together. But if you do manage to break it -- and even a small chip can disrupt that web of force -- the whole thing releases all that stored energy and explodes in a shower of little bits.