It's used in making crack.
Pyrex can be boiled without shattering, and as we all know, in order to make crack you have to put your cocaine/bicarbonate slurry inside a glass jar of some sort, then boil a pot of water with the jar in the middle. The slurry hardens into crack. Normal glass will shatter when you heat it like this, but Pyrex will not.
The wonderful thing about crack production is that with a bit of pyrex and a minimal amount of effort, you can turn 1000 dollars worth of cocaine into at least 2000 worth of crack. Maybe much more, I forget the numbers.
I wonder if this isn't a commentary on the modus operandi of the crack game as applied to fashion. Basically, Virgil Abloh is taking nickel & dime champion shorts, and with the help of a little pyrex, he's flipping them into a huge profit. He is the dealer, and we, of course, would be his customers. -poet on Pyrex