Every night around the world, millions of families sit down to a hearty pasta bake or casserole cooked in trusty Pyrex cookware. It’s a kitchen workhorse – hardy, easy to clean, delivering great results every time. And can you even call yourself a home cook if you don’t own one of those iconic measuring jugs? But it turns out that your Pyrex might not be Pyrex. At least, it might not be the Pyrex you think it is. And it all comes down to a matter of font. You see, there’s pyrex, and then there’s PYREX. Confused? So were we. So we did some digging. 

Related story: 25 retro kitchen relics every Aussie remembers (and your parents probably still own)

What’s the difference between pyrex and PYREX?

The key difference between pyrex (lowercase) and PYREX (all caps) is the material they’re made from. PYREX is made from a special thermal-shock-resistant borosilicate glass that was developed by Corning Glass Works (now Corning Incorporated – the company that invented the original CorningWare) in 1915. This type of glass handles extreme temperature changes better. So, for example, it could go from the freezer to a hot oven without cracking. 

Lowercase pyrex is made from what’s known as tempered soda-lime glass. This type of glass is stronger and more shatter-resistant if it’s dropped. It’s also more environmentally friendly, as it requires less energy to produce and, unlike borosilicate glass, it does not require the use of boron, a chemical that is strictly regulated and more hazardous to dispose of. However, soda-lime glass is more prone to shattering from heat stress. 

Credit: News Corp

Lowercase pyrex was also developed by Corning Glass Works, but this is where it gets confusing – the lowercase pyrex logo was officially introduced in 1975 as part of a rebrand to ‘modernise’ the look of the products. But the company had begun using tempered soda-lime glass in some of its products as early as the 1940s and ’50s. 

It wasn’t until 1998, when Corning decided to get out of the kitchenware business, that a line was drawn. In the US, Corelle Brands began producing lowercase/soda-lime pyrex products, while in Europe, the Middle East and Africa, International Cookware began producing uppercase/borosilicate PYREX products. The idea was that US home cooks were more likely to cook at lower temperatures and drop things, while European cooks were more likely to cook at higher temperatures and do more freezer- or stovetop-to-oven transitions. 

Related story: Uncomplicated one-pan recipes for an easy start to the week

So which type of PYREX/pyrex should I use?

Use your uppercase PYREX for more heavy-duty cooking jobs, like prepping a lasagne, freezing it, then transferring it to a hot oven. You should also use this type of PYREX for high-heat roasting, or pouring hot liquid (like boiling water or hot stock) into a room-temperature measuring jug. (Note: regardless of the font, you should never use glass bakeware on direct stovetop heat, and you should always place hot glass onto a dry towel or wooden trivet, never directly onto a cold stone or wet benchtop.)

Because this type of glass is less likely to shatter, use lowercase pyrex for your more rough-and-tumble jobs. (Clumsy cooks, this is great for you.) It’s great for cooking with kids, and is also good for low-and-slow cooking and reheating things in the microwave. 

Ultimately, whether your dish screams PYREX or whispers pyrex, you’ve got yourself a quality piece of cookware. Now go forth and get baking.

Related story: We’ll never stop crushing on these viral Le Creuset releases