Popular Science had an interesting blog post on how the change in manufacturing of Pyrex made crack production more difficult:
When World Kitchen took over the Pyrex brand, it started making more products out of prestressed soda-lime glass instead of borosilicate. With pre-stressed, or tempered, glass, the surface is under compression from forces inside the glass. It is stronger than borosilicate glass, but when it’s heated, it still expands as much as ordinary glass does. It doesn’t shatter immediately, because the expansion first acts only to release some of the built-in stress. But only up to a point.
It’s an interesting story, and the video is pretty great.
[Story via Schneier on Security.]