My hands are covered in remnants of Polyfila Expanding Foam Filler. It doesn't come off apparently. While reading the paper on the train this morning I was conscious that anyone sitting nearby would've assumed I had some kind of hideous skin condition. I also scratched my nose while this was setting on said fingers, and had to shave hardened foam filler of my nose, which is now red with some minor lacheration.
I also got some paint in my eyes.
The lesson is, never try.