Folbot used a woven fabric with some sort of plastic or vinyl laminate, which was probably specifically made for them. It was pretty shiny and slick on the outside. Kleppers used a grey fabric on the bottoms which was a neoprene or Hypalon impregnated (like rubber rafts have) woven material. The tops were canvas (usually blue). Top of my head, I don't remember whether it was cotton, acrylic or polyester canvas. It may have even been a vinyl-backed canvas like convertible tops use, but it's been too long since I assembled one. No filler or paint was used on any of the above. There used to be plans advertised back in the old days for some rather simple skin on frame kayaks (Sitka brand kayaks, for example) which used regular canvas and then house paint for the sealing. As far as I know, typical canoe filler is too brittle to hold up well on a suspended skin on frame construction.