Why Is Pyrex Exploding?

Hardly. Borosilicate glass has a very low thermal expansion coefficient compared to soda lime glass. Which translates into much lower mechanical stress due to temperature gradients.

This is why laboratory glassware is made from borosilicate glass. Such glassware can safely be held in a flame (kitchen: stovetop use), which is not safe with soda lime glass (tempered or not).

Breakage of soda lime glass may happen due to this difference in material properties.

For example: an oven dish 'burns', what do people do: rush it out of the oven (no problem), place it on a towel (no problem), or dump it in the kitchen sink. In the latter case: oven-temperature glass on ambient temperature metal plate. Bonus points if kitchen sink is wet for improved contact.

This "water splashes in sink" (or on kitchen countertop) causes certain areas of the oven dish to go to near-ambient temperature, while rest of the dish remains at near-oven temperatures. This is what causes difference in thermal expansion -> mechanical stress -> breakage. Small puddles of water in sink or kitchen counter are easy to overlook when someone's in a hurry because smoke comes out the oven. :-)

Hence the advice to place oven dish on DRY surface that conducts heat poorly, like towel, wood, or silicone sheet.

Borosilicate glass is much more likely to survive this type of abuse.

Note this says nothing of mechanical abuse like chip damage / scratches, dropping on the floor, hitting other objects, or some combination thereof. Tempered soda lime glass may well have an advantage there (but any object & its material has its limits of course).

And when it doesn't, borosilicate too can shatter due to thermal shock. Hence, "Don't forget that borosilicate glass also cracks with thermal shock".

Here's the Consumer Reports article on the topic back from 2013, at https://web.archive.org/web/20130430032310/http://www.consum...

"""We baked at least five samples of each brand in a 450-degree oven. All of the U.S. Pyrex and Anchor dishes shattered when placed on the wet countertop. None of the European dishes made of borosilicate broke, except one practice-run Arcuisine Elegance dish that had been through two baking cycles in our lab. At 400 degrees, we tested two samples each of the U.S. brands against two samples of Arcuisine. All of the American-brand dishes broke but the European brand did not.

When the oven was turned up to 500 degrees, all three of the European Pyrex dishes broke and two of the three Arcuisine dishes broke. We also tested a decades-old Pyrex dish in like-new condition given to us by a staff member's mother. Made by Corning of borosilicate glass, it didn't break, even at 500 degrees"""

The European Pyrex dishes were made of borosilicate glass.

To be very clear, these temperatures are extremely high, and "the test was contrary to instructions on the back of the label." The goal of the test was to see what the safety margin might be for cookware which might get scratched or damaged over time.

> Tempered soda lime glass may well have an advantage there (but any object & its material has its limits of course).

The sources I pointed to say it does have the advantage, and that advantage outweighs the thermal shock advantage.