The War Against Pyrex

Chances are, somewhere in your kitchen, you have a version of the measuring cup pictured above — if not multiples. Pyrex-brand measuring cups are incredibly common because they’re made to withstand thermal shocks — that is, you can use one to measure hot water and, immediately after, cold water, and they won’t likely break. Try that with a regular glass and you’ll find it, in shards, all over the floor.

For decades, Pyrex was made of borosilicate glass, a special type of glass in which boron oxide is added to the mix. The added boron allows Pyrex to handle heat much better than typical glass, so Pyrex is commonly found in kitchens, laboratories, and in use with aquarium heaters (as the heaters are, necessarily, submerged in much cooler water). But in 1998, Corning, the company which made Pyrex, sold the brand to World Kitchen LLC. World Kitchen decided to stop the manufacture of borosilicate glass, and since then, Pyrex sold in the United States is made of tempered soda-lime glass, which does not handle heat as well as borosilicate glass does. (It may, however, be more resilient to drops.) In most cases that does not matter much, as tempered soda-lime glass is still pretty good at withstanding thermal shocks.

But it’s not great. In 2010, Consumer Reports (as reported by its quasi-independent blog, Consumerist), tested some Pyrex and and found that taking the newer glass out of a hot oven and placing it on a wet granite countertop yielded poor results: the glass shattered almost instantly, and violently so. (There’s a video at the Consumerist link). And as Popular Science demonstrated, super-heating a measuring cup (in their case, with a blowtorch) and then adding just a drop of water has a similar effect — shattered glass, everywhere. Test tubes in chemistry labs are still made of borosilicate glass to avoid this very problem.

Of course, there are few cases where one is going to expose a Pyrex measuring cup to such extreme temperatures, so, if you do have a soda-lime one in your kitchen (and you probably do), there is little reason to worry — your recipes are almost certainly safe. Even the restaurant and food services industries can use the newer version of Pyrex without much concern. But one industry was struck very hard by the switch: the crack cocaine trade.  It turns out that turning cocaine into crack requires bringing the solution of water and powdered cocaine to a very high temperature and then rapidly cooling it. And for years, crack makers would use Pyrex — borosilicate glass ones, that is — to accomplish this step, successfully. The soda-lime glass alternatives cannot withstand the thermal shock.

As a result, the drug trade needed to find another way to obtain borosilicate glass. The unintended consequence of World Kitchen’s switch? An uptick in theft from an unlikely place. As PopSci so eloquently notes, “[the crack-making] industry was forced to switch from measuring cups purchased at Walmart to test tubes and beakers stolen from labs.”


Bonus fact: Fill a bowl with Wesson brand vegetable oil and dip a (borosilicate) Pyrex test tube in it — and the test tube will disappear, as seen in this video. What’s going on? The oil and test tube have the same indices of refraction; that is, the speed of light passing through either medium is identical. As light is not refracted nor reflected as it passed from the oil to the test tube, the test tube seems to disappear before our very eyes.

From the ArchivesHalf Baked: How crack cocaine led to the war against baking soda.

Related: The crack makers are trying too hard if they’ve turned to theft in order to get borosilicate glass. You can buy a ten pack of such test tubes for $10.99 with free shipping via Amazon Prime.