So, I have a few foils that I haven't even tried. They look amazing before top coat and start crinkling the minute you try to cover them :( I tried using the special sealer on top, didn't work for me. I also tried a few top coats (Seche Vite, Good to Go, Super Shiney, Ibd for polish, Nubar diamond and others) but they all seemed to damage it. I also tried applying an extra coat of adhesive on top of the foil, so that there would be no immediate contact between topcoat and foil, the damage was much less. I heard that airbrush sealers work best, you mist it on the foil and let it dry. Then you top coat. I do not own any airbrush material, so I wouldn't know.. Soak off gel worked best for me, especially the CND Shellac one, you can see on the pinky, the damage is hardly noticeable :)
Topcoats that failed to pass the test:
What do you use to seal foils?