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Anyone who's purchased Pyrex products in the past 20 years ought to know what's changed. 

By Maggie Burch

Any cook worth her salt knows and trusts several brand names when it comes to cook- and bakeware that gets the job done better than anything else. Along with Le Creuset and Calphalon, Pyrex is one of those relied-upon brands for everything glass, from measuring cups to casserole dishes. The brand has been around for over 100 years, and has established a reputation based on its material that was strong enough to be used in kitchens and laboratories alike. What you may not know, though, is that Pyrex goods made in the past 20 years are manufactured differently than they used to be, and as a result, are no longer as resistant to extreme temperature changes as they once were.

For the first 90 years of Pyrex’s history, its glass bakeware was in a league of its own because the products were made with borosilicate glass, which is thermal-shock proof. Meaning your casserole dish could safely go from the icebox to the oven, and back again. Unlike other glass and ceramic cookware, Pyrex dishes could withstand extreme temperature changes, which made them a kitchen standby. Around 1998, though, Pyrex quietly switched from making its U.S. products with borosilicate glass to tempered soda-lime glass, which is still fairly durable but is not thermal-shock proof.

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Consumer Reports first reported on this switch after several customers claimed that their Pyrex dishes exploded or shattered either in the oven or after removing them from the oven and putting them on a wet, cold countertop. It’s a dangerous situation that could more than just ruin your dinner, and we hope anyone reading this is able to avoid a similar disaster. Here’s what you need to know:

If you’re sure your Pyrex dishes are more than 20 years old, perhaps you already knew you might have some valuable heirlooms in your cabinets, but now you can know they’re even more valuable for their durability and safety in the kitchen. If you have purchased Pyrex in the last 20 years and haven’t yet had an incident of any glass shattering on you, you’ve likely already been exercising caution, but know that you shouldn’t push the limits of your bakeware. Pyrex does in fact list on their website several things to avoid doing with their products, including not adding liquid to hot glassware. If you’re taking a casserole dish out of the freezer or refrigerator, let it sit out and get closer to room temperature before putting it in a preheated oven, and do the opposite when putting leftovers away.

Because the manufacturing process was changed due to an ownership shift over American-manufactured Pyrex, there are Pyrex products still made with borosilicate glass in Europe that you can purchase on Amazon and other websites if that safety element is important to you. Otherwise, you can search Ebay and other resale sites for vintage Pyrex—just don’t be alarmed by the prices. We told you, this stuff is gold.