Mostly availability of sheets, but i find out that using thermocol alone is not as tough as the mix, using depron on base makes wing much tougher and thermocol should be mostly used on top for giving it shapes (airfoils).

  great improvisation there.

Can you use thermocol in making the wing? Great, but of what density and how?

just normal thermocol, any craft thermocol.

EDIT: image updated