Foam sheeting vs, Ribbed
 

What would weigh more, A foam sheeted wing or one that was ribbed out.

Foam sheeting vs, Ribbed
 

Depends on the technique and materials used. Could be either one. My buddy who builds some big ones for me once in a while is building me an Edge right now with a new wing technique. Uses a wing jig to hold blocks of foam - puts templates on each end and cuts them like you would a foam blank, except these are now foam ribs - puts spars - wing tube - carbon fiber - all as needed and sheets the thing. Strong as any other technique and don't weigh nothing.

Dan

Foam sheeting vs, Ribbed
 

The only foam wings I have built are on gliders. They are exceptionally strong, straight, and light. Also, most all of the F3A and advanced IMAC pilots are using foam wings. You really have a lot of freedom in the construction details. Here is a short list of options from my limited experience:
1) Foam density, 1lb, 2lb, 3lb/cubic foot. (white, pink, blue)
2) Sheeting, balsa, obeechi, glass, carbon, or any combination.
3) Spar, wood, wood wrapped with carbon filament, no spar at all.
5) Adhesive. I always used epoxy to avoid warping but others have used plain wood glue, spray adhesive, polyurethane, double sided tape.
6) finishing, plastic covering, paint, none/natural.

Even though most of my planes have rib wings (kits and ARF) I firmly believe that a superior wing can be made using a foam core or molding process.