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I Just Found Out My Pyrex Isn't a Real PYREX and My Mind Is Blown

May 25, 2024May 25, 2024

Exploding lasagnas are no fun, so here’s how to differentiate between Pyrex products.

Eleanor is EatingWell's editorial apprentice. She attends Iowa State University, where she is a junior studying journalism, political science and history. During her time at college, she has worked as an editor and reporter at the campus newspaper, the Iowa State Daily, where she wrote about culture and lifestyle. She is an editorial director at TREND Magazine, an on-campus fashion publication.

Pyrex containers are a staple in many kitchens. I grew up baking casseroles in the containers and warming up leftovers in the microwave. So, when I found out that there is a difference between the products labeled "PYREX" and "pyrex," my head immediately started to hurt.

Facebook pages, TikTok and Reddit threads are teaching us that the difference between "PYREX" and "pyrex" is super important to understand in order to keep your food safe and containers in good condition.

"Pyrex" is the official, trademarked brand name of the popular cookware brand. When the "P" is capitalized and the rest is lowercase, it is simply a proper noun for the company. The business got its name by spinning off its original product, the "Pyright" pie pan.

Little-p pyrex is probably what your kitchen's measuring cups, meal-prep containers and drinkware are made from. It's crafted from soda-lime glass, one of the most common types of glass produced commercially. Soda-lime glass is less expensive because it's not as heat resistant. In fact, it's used for products like light bulbs and some beverage bottles because of how easy it is to mold into shape while hot.

The brand, Pyrex, has historically owned the trademark for little-p pyrex, but its parent company, Corning, has since sold it. Lowercase "pyrex" is produced by other cookware companies that don't use the heat-resistant borosilicate glass the original company does (more on that below).

Since, pyrex (emphasis on the lowercase letters) is mostly made from soda-lime glass, it is definitely not recommended for use in the oven or microwave. Some social media users have even shown instances of their pyrex containers blowing up in the oven.

Big-p PYREX is made of borosilicate glass, which is much more heat-resistant and durable than other kinds of glass. That makes this a good material for making cookware and microwaveable containers, plus you can feel safe adding hot liquids to measuring cups made from it or using those measuring cups in the microwave.

Composed of silica and boron oxide, borosilicate glass is much more suited for high-heat cooking. The boron oxide in the glass strengthens and reinforces the chemical structure of the glass, making it especially tough against high temperatures. Borosilicate glass was the original material Pyrex used to make its cookware, and many of the brand's products are made of the glass today.

The next time you go to cook dinner in a Pyrex pan, take a look at the labeling. Cookware with lowercase logos are usually made of soda-lime glass and should not be heated up in the oven or microwave to minimize risk of them breaking. Cookware with logos in all-caps are typically made of borosilicate glass and can be heated at high temperatures without harm.

Pyrex is a household name, and lovers of the classic cookware can rest easy tonight knowing how to avoid glass in their delicious pan of brownies. To help you keep all the different variations and definitions of this cookware lesson, here's a cheat code:

To ensure that your kitchen stays safe and your cookware stays in one piece, never put pyrex or PYREX under a broiler because the intense heat may fracture the glass. You should also let refrigerated glass sit at room temperature for 30 minutes before putting it in the oven. Pyrex containers of all kinds are best for food storage, and cooking your meals in oven-specific cookware is always a good practice.

So now that you understand the differences between the home cook's favorite cookware, get cooking! With the right kind of container, of course.