My experience so far is positive. I found it to be very hard, yet seems to be still flexible enough for our use. I sand it with 320-400 where it flowed perfectly (most of the areas), and smoothed it out with 150 where it needed more smoothing. Then went over it again with 220 then 400. IMO, it sands remarkably well for as hard as it is. This is all over balsa so far. I can see where you may, as he states, want a second coat over foam, but keep in mind, the need for the surface prep with the filler 'slurry" for best results. I can't wait to use it on a Depron plane. With a hard shell of this stuff and Testors spray paint, my jets will look so much better. As I now have the stuff on hand, I see myself finding more ways to use it. Maybe even molding small parts for cockpits, for example.