Center Console Boats And More

What is the most bouyant material known to man?

Ok, here's the scoop. I learned about SWATH type submerged hull boats. It seems to me that the "pontoon" shaped submerged hulls should be made of the most bouyant substance available, but I haven't been able to find out what that is. Polystyrene foam would almost certainly work, but is there any better option?