World War II era alternative materials for construction (not counting common metals and woods used in aviation)?

[BarnOwlLover]

What were some that were proposed, and what was their possible viability and challenges? I'm of course not counting things like aluminum or steel alloys, or woods common in aviation use. And yes, I know also about the Aerolite Spitfire, which showed that it was possible, but how viable would it (or anything else) have been?

 

[Capt. Vick]

The Budd Conestoga was made from welded stainless steel...