: Has anyone used polystrene as boatbuilding foam?

My experience with polystyrene, epoxy, kevlar & glass used to make sail boards was that the PS foams did not have enough edge strength to hold up to the loads of wave sailing, in particular wave jumping. A layer of 6 oz. kevlar however, made them indestructable even when the whole bottom was flapping loose from the foam.

I would expect that kayaks are less heavily stressed than a sailboard so I would not worry too much about it. The main thing would be to put enough glass/kevlar on the exterior so that it is pretty much the single skin of glass that is doing the work and to not really too much on the foam other than to give the boat shape for glassing. Some testing of panels would probably suffice to design a layup. My very unscientific method is to layup 1' x 1' test panel and after they are well cured, I start smacking with various size hammers including a 16 oz, a 3 lb and a 6 lb sledge. Each of these will give you a sense of just how tough your laminate will be. Very little is needed to just hold shape and keep the water out. More is needed is you intend to bounce the boat off rocks. My sailboards with one 6 ox. layer of kevlar and one 6 oz. layer of E-glass were very rock proof.

Craig