Why foam? Foam is very lightweight and easily repaired. But foam is flexible so wings will require support spars to add rigidity. Spars should be preferably fiberglass or carbon fiber, not metal. Carbon spars might mess with the antennas because it is conductive, they “might” interfere antennas depending on wavelength.
Foam is great for planes under 10 pounds est. all up weight, after that you will need more support. Then you will need carbon fiber and kevlar to keep all the bits together, that’s when things get complicated.
EPP – Expanded Polypropylene foam. Commonly used in electronics packaging, this is the type of foam that your hard-drive or a new laptop computer is shipped with. Durable, flexible. Handles impact very well. The best choice, but very few planes are made of this new foam. ex: Ritewing Zephyr 1 and Ritewing Quadspar
EPO – Expanded Polyolefin foam. Similar to EPP but not as flexible. Stiff, durable. Handles impact well. Second best, most modern foam planes are made of this. Easily molded and because of that and just about every other RC airframe is made of it. ex: Ritewing Zephyr II, Bixler.
EPS – Expanded Polystyrene foam. Think disposable coffee cups, meat trays and surfboard foam. Brittle, very lightweight. Dents or breaks on impact. ex: homebuilts
XPS – Extruded version of EPS. Blue or pink foam board insulation that is available at home improvement stores. Brittle, lightweight. Dents or breaks on impact. Also called Depron. ex: homebuilts
Foam wings are recommend to be covered with shrink covering, and put packing tape on leading edges. Helps in durability for crashes.
Ritewing ZII…EPO with fiberglass spar visible: