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/mÃ‚Â³.
And yes, okay, it absorbs water...
... when your board is broken, and this situation is not supposed to happen.