What's the Difference Between PYREX and pyrex?

Anytime I scroll through Facebook Marketplace, I see tons of people selling vintage Pyrex dishes. These retro baking dishes are obviously super cute—I actually have my eye on a pink floral set on Etsy — but aesthetics aren’t the only reason people are willing to spend big bucks on old-school Pyrex. 

Turns out, not all Pyrex is created equal, and the older stuff is better than newer-made products for an important reason. There are two different types of Pyrex: all-caps PYREX, and all-lowercase pyrex. There’s a key difference between the two products, so if you have any in your kitchen, you’ll want to take stock of your collection — and if you’re thinking of investing in some, be mindful of what you’re purchasing.

The Difference Between PYREX and pyrex

The history of Pyrex goes back farther than the 1970s casserole dishes you’ve seen on Etsy. Way back in 1915, Corning Glass Works — now Corning Incorporated — developed its first consumer cooking products. The product started as a solution to a problem the creator’s wife experienced in the kitchen: Her casserole dish cracked when she was baking.

Guide to Vintage Pyrex Patterns

Until around the 1950's, all Pyrex products were made of borosilicate glass, which is resistant to thermal shock, a rapid temperature change that can cause something to explode. Corning started producing tempered soda-lime glass at some point in the 1950's but it's not clear when they started the transition. When Corning sold the brand in 1998, the new company making it in the United States claims that soda-lime is as safe as borosilicate glass.

Soda-lime glass is cheaper but doesn’t have the same thermal shock-resistant properties of borosilicate glass. That’s why so many people report their Pyrex exploding in the oven or due to extreme temperature changes (for example, placing a very hot dish on a colder surface). 

Here’s where the branding comes in. All-caps PYREX, which is sold and made in France, is still made of borosilicate glass. But any Pyrex that’s all lowercase — a recent change in branding — is soda-lime glass, which isn’t designed to withstand drastic temperature changes.

Manufacturers say soda-lime glass has advantages; for example, it may not break as easily if you drop it. But according to Consumer Reports testing, soda lime dishes are more likely to shatter than their borosilicate counterparts.

Safety Tips for Baking With Pyrex

Checking what kind of Pyrex you have is the first step. According to the manufacturer, lowercase pyrex can still go in the oven, but with some serious caveats, which are listed below. If you have all-caps PYREX, your dishes should be able to withstand more drastic temperature changes, but the below steps are still worth following for peace of mind: 

• Always preheat your oven fully before putting the baking dish inside, because glass is more likely to shatter if it’s exposed directly to the oven’s heating element. 
• Never place any kind of Pyrex on the stovetop. 
• Always cover the bottom of your glass dish with liquid before cooking meat or vegetables in it.
• Always avoid putting a hot dish directly on the counter. Instead, use a trivet or potholder. 
• Don’t add any liquid to hot glassware.
• Don’t take dishes directly from the freezer or refrigerator to the oven (or the other way around). 
• Don’t use chipped, scratched, or damaged bakeware, which, according to Consumer Reports, is more likely to shatter.

As with any kitchen-related product, be sure to read the instructions and safety warnings carefully before using it. If you want to be extra safe, then your best bet is to use metal for baking instead of glass. That cute vintage Pyrex set can still come in handy for serving and storage!