At least for Samsung, when you first turn it on, you get a nice big warning that says the phone is not dust or water resistant, and that you can damage the screen with sharp objects, like your fingernail. [1]

I tried one and permanently dented it on accident with the stylus. Can't image what would happen if you did something crazy like go to a beach.

[1] https://www.reddit.com/r/GalaxyFold/comments/1vhhow0/because...