Why Are Pyrex Dishes Exploding?

There I was, minding my business while baking a delicious sweet potato casserole topped with roasted marshmallows. I’ve made it a dozen times before (recipe coming soon!) with my trusty loaf pan that was also used for casseroles, breads, and even cornbread.

I took it out of the oven and placed it on the warm stove top to cool. Again, something I’ve done plenty of times before and didn’t think twice about. I turned my back for one second to grab something and that’s when I heard a crack.

Taking a closer look and sure enough, there was a hairline crack on one end of the dish. While inspecting and trying to figure out if my casserole is a lost cause, things were looking hopeful when all of a sudden…

💥 BOOM 💥

Pyrex Casserole Insta

My loaf pan was made of Pyrex, and after doing some digging, I found an interesting story that explains why their glassware is randomly exploding / shattering to pieces while cooking.

Why is Pyrex Glassware Exploding?

The culprit behind the mystery is thermal shock, which is the direct result of rapid temperature changes. When glass is heated or cooled too quickly, different parts of the glassware expand and contract. This stress degrades the structural integrity of the dish and results in the glass breaking apart in a spectacular fashion – popularly known as “exploding”.

Thermal Shock

A large and rapid change of temperature considered especially with respect to its effects upon living organisms or structural parts.

Merriam-Webster

But isn’t Pyrex Made for That?

That’s the caveat – it used to be. Here’s a quick history lesson on Pyrex cookware:

Once upon a time, Pyrex was spelled PYREX (in all caps). It was a popular cookware brand made out of a material called borosilicate glass. This type of glass is extremely resistant to thermal shock, which made it ideal to use as cookware over other glass and ceramic options.

At some point, PYREX changed their name to Pyrex, and with that came a new ingredient to be used for their cookware line: tempered soda-lime glass. Presumably a cost-saving method, because soda-lime glass is much less expensive than borosilicate.

Unfortunately for consumers, a cheaper price tag also means a lower quality product, since soda-lime glass is much less resistant to thermal shock than its more durable counterpart. It’s also interesting to note that Pyrex is no longer made or owned by the original manufacturer.

Pyrex vs PYREX

No one knows exactly when Pyrex made the switch. Some speculate that it was soft-launched sometime during the 1950s, while others suggest the change was official in 1998 when Corning, the company that made PYREX, sold the brand to World Kitchen LLC and PYREX became Pyrex. Practically all glassware sold in the U.S today is made with soda-lime glass.

Because of this, all original PYREX cookware is considered vintage and comes with a hefty price tag depending on how decorative it is. In 2017, someone paid almost $6,000 on this Lucky in Love  PYREX dish!

To make this even more scandalous, another unexpected consequence of the ingredient switch is that the illegal manufacture of crack cocaine is much more difficult with soda-lime glass than borosilicate, which is commonly used as lab equipment because of its high resistance to thermal shock. Who would’ve thought?

Don’t Throw it Out Just Yet

If you have Pyrex cookware that’s made with soda-lime glass, don’t fret! There are ways to prevent thermal shock from happening so you don’t have to throw out your cookware and go hunting for replacements.

The easiest and best method is to avoid sudden changes in temperature. Don’t take a hot Pyrex dish straight out of the oven and put it in the fridge or freezer – and vice versa. Take care when pouring hot liquids into glass measuring cups and allow the dishes to cool before submerging in water.

With that being said, I did all of the above things and my loaf pan still exploded 🤷‍♀️. I’ve had it for many years and maybe it was just old and degraded over time. Now I’m just being extra careful with my current dishes and hopefully I can avoid any more kitchen mishaps 🤞.  

Have any of your Pyrex dishes shattered or exploded while cooking? Share your experience in the comments below!

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