: Cardboard on edge is pretty strong for it's weight, I'd bet
: stronger than balsa. I suspect he did it for the style rather
: than proving a point.

: Bill H.

It is also probably one of the cheapest materials for prototyping, process development, etc.
He has been through the "NC machine tool home school" edu experience with this, as well as
learning to glass across voids.
I don't know, I haven't done it, but I suspect that there is a need for a fine touch in the glassing technique.
Just pulling the cloth a little bit with the spreader is probably very different on all those vertical edges than
pulling it a bit on the solid surface of a strip built hull or foam board core.
Well, pulling it a bit might be the same, putting it back would not be (-:

Drilling out a foam core for weight savings ?
I don't know what you would need for minimum wall thickness, or how big of a hole you would be comfortable glassing across, but 1/2 inch web (at its minimum point) between 2 inch diameter holes would take out about 58% of the material in the main field, less towards the edges, assuming you would want to leave more material there.
I have NO idea if those dimensions would work, just playing with the arithmetic.
Going to 1/4 inch between takes out about 71.x%

I might take a hole saw to some 2 inch thick pink insulation foam that I have left over, then see if I can glass across a honeycomb - probably not (-: