Is lowercase pyrex glass measuring cup different than uppercase?

Uppercase PYREX → usually older, made from borosilicate glass (more resistant to thermal shock).

Lowercase pyrex → newer, made from tempered soda‑lime glass (still durable, but less resistant to sudden temperature changes).

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DunningKruger · 61-69, M

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.