foam weighs one pound per cubic foot.
You are lucky to scoop out an ounce - if you leave in torsional resistance.
It is the least effective weight reduction method.
The strength drops faster than the weight!
Thick stuff - yes - double cut the wing -one outer cut -one inner cut.
here is the tricky part
make the inner cut with a little bit of draft -such that you can re-insert the center and it will slide in tightly
Now - slice off a few 1/2" wide ribs -from the cente cut - wet them with a mix of ProBond and water and slide em into place
This is effective weight reduction as the strength is still good .
but under a 12% airfoil - fer get it