The resin is used to make a mold for silicone by inverting the 3d model, I’ve done it for a couple of pipe ideas before to see if they’d be cool (I’m bad at 3d design is what I learned)
I also know a guy who uses some EXPENSIVE resin that’s apparently safe to use in medical situations, so I assume breathing through that once it’s done with its treatment is probably fine, but I’d never do it with my cheap shit, even being in the room with it hurts with my mask on (hyperbole)