Surprise! Pyrex and PYREX Are Different

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.

What Is Pyrex?

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.

What’s the Difference Between Pyrex and PYREX?

The major difference between lowercase Pyrex and uppercase PYREX is the name. But it’s also the material they’re made from. While lowercase Pyrex—which is the stuff you see in stores in the United States—is made from soda lime, uppercase PYREX is made from borosilicate.

While all Pyrex used to be made from borosilicate, the brand appears to have made the switch sometime in the 1950s, according to The New York Times. However, the brand hasn’t made an official comment on why the switch occurred.

However, it’s important to note that this switch was only made in the United States. In Europe, PYREX made from borosilicate is still available.

What Is Pyrex Made Of?

So, what is Pyrex made of?

Old school PYREX and the PYREX sold in Europe are 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. So, when you see the capital letter PYREX, it’s likely made of borosilicate and less likely to break.

In lowercase letters, Pyrex 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 that 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? Technically, PYREX is no longer sold in the United States. Instead, the brand sells lowercase Pyrex, the soda-lime product. Any PYREX product is likely vintage and 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.

Does Pyrex Explode?

So, if you’ve ever been scrolling through TikTok and found yourself either laughing or gasping when people take a Pyrex glass dish from the oven only to have it “explode” on them, you can be certain it’s not PYREX, which was less likely to break under the pressure of temperature swings. Of course, that’s not really the safest option when it comes to how to tell if Pyrex is 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 lowercase Pyrex. But, if you really want to know how to tell if Pyrex is borosilicate, look at the edge of the dish. If it has a blue-green hue, it’s made of soda-lime.

So, will Pyrex made of soda lime explode? It can, yes, but it is highly unlikely. Southern Living spoke with a Pyrex representative who explained that less than one tenth of one percent of the Pyrex sold every year will have breakage.