You likely know Pyrex thanks to the brand’s iconic glass measuring cups and beloved casserole dishes. Turns out, though that those iconic items aren’t always the same. There’s Pyrex and PYREX, so what’s the difference?

The difference between Pyrex and PYREX is all about the type of glass used to make the cookware and bakeware.

Pyrex has long had a reputation for being, well, explosion-proof. The cookware is known for its ability to move seamlessly between hot and cold temperatures without cracking. However, thanks to social media documentation, people have begun to see Pyrex dishes crack under extreme temperatures, and the type of Pyrex might be why.

The bakeware of old is PYREX with all capital letters. It’s made of borosilicate which is comprised of boron trioxide and has a low thermal expansion rate. Essentially, it can withstand temperature changes like going from oven to fridge without breaking. When you see the capital letter PYREX, it’s likely made of borosilicate and less likely to break.

Pyrex, in lowercase letters, is made from soda-lime, the same glass used to make many drinking glasses and other kitchen glassware. The difference is that Pyrex’s soda-lime is heat treated to become tempered so it can withstand temperature changes much better than your pint glass. While it’s still not common for a Pyrex to break, it’s more possible than if you use a PYREX.

But why do both even exist? Well, technically, in the United States, PYREX is no longer sold. Instead, the brand sells Pyrex, the soda-lime product. Any PYREX product is likely vintage and was thrifted or has been in your family for a long time. PYREX is also sold in Europe, Africa, and the Middle East, so if you’ve bought bakeware abroad, it could be made from borosilicate.

If you’re ever on the hunt for new cookware and stumble across some PYREX in a thrift store, yes, it is different than your home goods store’s Pyrex.