It's written on parchment[1], I've found mentions that the _drafts_ were on hemp paper but not a firm source on how we know this or where these drafts are now.

[1] https://www.archives.gov/preservation/formats/paper-vellum.h...

Source for this? A little searching is telling me this is a myth.

How about a source that disproves it entirely instead? https://www.usconstitution.net/constfaq_q145.html

> How about a source that disproves it entirely instead?

As pointed out in your link, the copy in the National Archives isn't written on hemp, but the first drafts of the Constitution - ie, as it was literally being written - likely were.

OP misstated it slightly, or in a way that's a bit misleading, but it's not incorrect.

Maybe the grand-parent meant the people who wrote the constitution were stoned.