It's also important to know that not all foam is created equal.

When you wonder if foam is as weak as balsa, you're no doubt thinking of the very light weight white beaded stuff.

We are using pink or blue foam (dow hi-load or owens corning foamular) rated from 25 to 60psi depending on the plane and the designer. Most common in is 40psi foam. 40psi foam is hard stuff.

When someone does show up and try to fly combat with a balsa airplane, it's not uncommon for the eventual midair to blow the plane in to little bits, while the armored foam plane flys out with no damage. A couple of times I've flown though a balsa plane, and after landing, I couldn't even figure out where on my wing the impact was (excpet, maybe, for the paint smear).