I think about them constantly. I like to tinker and builds things, and I'm always wondering how do many props in movies can be so sturdy yet flexible or how someone's hat stays on their head in a scene.

Seems like a fascinating, fun world

Adam Savage's Tested Youtube channel is doing a series of videos right now on background props (any and all types of paper products, fake money, grocery items, etc). Apparently, up until recently, 1 company - Earl Hayes Press - has been responsible for production of these process for every major film for the past 100 years. The videos are really interesting if you're into that kind of stuff.

Here's the first video in the series: https://www.youtube.com/watch?v=0TS6x8dK2u0