Is lowercase pyrex glass measuring cup different than uppercase?

Pyrex is a registered trademark, a brand name owned by Corelle.

Lowercase pyrex is what's sometimes called a generified version of the brand name, the same way every facial tissue is "Kleenex," or you "Xerox" a copy, or you "Google" a term online. Companies hate this sort of thing, of course, because if it gets too common, they can loose their trademarks the way Thermos did in 1963.

That’s a deep dive