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A new borosilicate glass 8 x 8 pan arrived recently. It's not inexpensive, but it's also not cheap soda-lime junk either. It's French-made under the name 'Arcuisine' (evidently "European Pyrex" which is still proper borosilicate glass - good to 300 C which is 570 F, rather than only 425 F). I've now used it once and am so far happy with it.
I do not plan to abuse it like was done for these extreme tests but those do show that borosilicate will outlast soda-lime under extreme conditions.
It looks like right now if I want decent glass bakeware my choices are Arcuisine (French) or Simax (Czech). Both cost, but both are right proper borosilicate. So called "pyrex" (lower case) and Anchor are both now mere soda-lime and not worth bothering with unless I expect to never heat or chill them much. A "pyrex" mixing bowl is probably fine. A "pyrex" pan is wasted money.
I have two measuring cups. One is labeled PYREX (upper case) and is absolutely clear. It's older, and proper borosilicate. The other is newer and 'pyrex' (all lower case) and has the telltale green tinge of mere soda-lime glass. The answer is clear: I buy Arcuisine or Simax. World Kitchen (who bought the pyrex name from Corning) does not deserve my money - unless they start making things of proper borosilicate glass. Neither does Anchor Hocking, for the very same reason. Simple rule: Bakeware with a green tinge is crap - DO NOT BUY. Soda-lime won't always be given away by the green tinge, but if you see it, leave it on the shelf rather than waste your money on shatter-prone garbage.
I was unaware that Corning, or its inheritor World Kitchen switched from proper low-expansion borosilicate glass to ordinary (alright, tempered) soda-lime glass, which is not low-expansion. I just got to experience this cheapening. My 8x8 "Pyrex" pan went into the oven at room temperature and in one piece. It came out rather hotter (what's an oven for?) but in several pieces. Naturally, I am unhappy about this.
Pyrex had come to mean "can handle heat" and this utterly failed to. Now, borosilicate glass is not as low-expansion or change-in-heat tolerant as fused quartz, but I'm not going from boiling water to an ice bath (fused quartz can deal with that, borosilicate cannot). Soda-lime glass is very much not known for low-expansion or dealing well with changes in heat. The maker claims it's less prone to breakage when dropped. Also, it's cheaper to make. But that doesn't help it hold together when used for baking, which is rather the point of a thing called "bakeware."
Now, where do I get a right, proper borosilicate glass pan? After this, I am not sure I can trust any of this recent pseudo-Pyrex. I might end up preemptively replacing it all before I get a big mess. I was relatively lucky this time and only baking some fish - easy to recover for cleanup. Had it been a cake or brownies or something more fluid, I'd have had a much nastier mess to clean up.
