Square PVC rails?

[KeeoS]

guys,

I'm in the need of solid rails. I broke mine within a week and I'd be very glad if this doesn't occur anymore. So I've been thinkering on the plans of my next board...

Ideas:
* An outline in PVC hard foam (forex?) of 1,5cm.
* inner filled with balsa -the lightest I can find-
* deck, 1 layer of carbon and 1 of UD glass fiber.
* bottom, 1 layer of carbon-kevlar and 1 of UD fibers.

Now, I'm just wondering, I see a lot of square edges on formica-boards; It will definitely be more solid and easier to build, but does it have any drawbacks?
Should I use foam instead of balsa and why? and what kind of foam?
Any other ideas?

[psa]

shortly: foam is lighter than balsa. foam (80 gr/m3) divinycell and corecell. some foams are hard to shape, do not remember which ones. top 400 gr carbon + 200 gr glass + patches. bottom 200 gr carbon + 200 gr glass.

foams above do not suck water. balsa wood sucks water.

[Guest]

shortly: foam is lighter than balsa. foam (80 gr/m3) divinycell and corecell. some foams are hard to shape, do not remember which ones. top 400 gr carbon + 200 gr glass + patches. bottom 200 gr carbon + 200 gr glass.

foams above do not suck water. balsa wood sucks water.

Balsa is more solid than foam and it even exists in densities of 60gr/m³.
And yes, okay, it absorbs water...
... when your board is broken, and this situation is not supposed to happen.