Don't the so called "Ultra" layups on kayaks and surfskis such as Epic's be using foam core (e.g. "honey-comb" or whatever)? They are stiff and very light but easily punctured...

: Yes, you're correct. However, I don't know of any kayaks using foam core in
: their layups. Usually it's used on larger boats where the thickness is not
: an issue. They actually sell a polystrene foam that has a checkered
: pattern so it can easily bend in both directions. Actually foam core and
: balsa core is used on more expensive large boats because the cheaper way
: is to just use plywood which also adds weight.