Yep. Polyester film is not made to be painted on. I've done it once, made some stripes on the rudders of a foam park flyer. The rudders were built up and covered, while the rest of the plane was EPO foam. I scuffed it with steel wool too, and it held up ok. I could scratch the paint right off with my nail if I wanted to, but the rudders didn't see any wear. There's no way I'd do a whole plane that way though. If Steve has some pics of planes he's done with an all over paint job on top of polyester film I'd like to see it. Some data on the weight gain would be handy too, because I can't imagine a plane done that way coming out light.