I've tried balsa built-up, all foam, blow moulded, fibre glass - all have +/- 's - but work well too. It is important to glass cloth the bottom of balsa and foam floats - once had a balsa float holed by a submerged log (might have been a crocodile though !) and it started to sink pretty quick. So they get the F/G treatment now. Whatever type you decide to use, make sure 1/ you use waterproof glues (epoxy, Ca - not white glue) and 2/ all joints are tightly sealed (wing to fuselage joint and tank hatch - smear grease). Enjoy. MalcolmL