All my Isobars and DC-10s are 2 lb/ft^3 blue foam
with one layer of 2 oz glass. 2 layers of 2oz along
the trailing edge, but the key is 4-6 inch
wide of uni 6 oz carbon for a spar. Even in the
Isoburst years ago, the wing did not fail, it just
left the plane. All elevators are 1 layer of 6 oz.

But Kevin is correct, drop your keys on it and
it will crack.

My advice, if you want to make a stronger wing,
make it thicker. Every time you double the thickness
of a wing you increase the strength by ~8 times.

Hope this helps..

Eddie Weeks