Whenever I see load-bearing cardboard like this one from Macskyver's build, I always try to find a use for it:

I have heard many times of going into stores and asking for old boxes, but my wife works retail, and when we moved, I brought home 25 boxes.
I can't imagine removing tape and staples, cutting boxes into 3.45" strips, gluing them into a stack 1.45" thick, and wrapping them in fiberglass and flame-retardant resin, but it should still be fairly strong, and insulate better than wood.
It wouldn't flex like wood, though.