We should observe Canadian John’s safety drill…avoid extreme temperature changes. Let hot Pyrex cool to near room temperature on a cooling rack or potholder before washing, refrigerating, or freezing. Don’t place freezer or refrigerator-cold Pyrex where it will be heated, such as the stovetop or oven.
Southern Living magazine had an article on Pyrex glass a while back that says that old Pyrex (made before 1959 or so) was borosilicate glass and was amazingly resistant to thermal breakage, but somewhat brittle, and the newer formula is tempered soda lime glass. It’s not nearly as susceptible to breakage from drops or blows and is still thermal shock resistant. Hmmm, view this with skepticism.
The author says a Pyrex company spokesperson stated that less than one-tenth of one percent of millions of Pyrex goods sold each year result in thermal breakage. (I don’t know about Pyrex, but I think that other companies have intentionally deceived us.)