That's not entirely correct. The paper that US Currency is printed on is a linen-cotton blend, but it's still considered a "paper", even though it doesn't come

That's not entirely correct. The paper that US Currency is printed on is a linen-cotton blend, but it's still considered a "paper", even though it doesn't come from trees. There was a fascinating article about this on Planet Money a few weeks back, including an interview with the head of Crane's, the company that provides the source paper to the US Mint.