Scioly.org

We are building an arch bridge and were wondering if it is legal to use cork? Thanks in advance!

Last year, cork was not considered to be a wood. Technically it is bark of a particular tree. One possible reason might be that a lot of cork board is a composite.
To me, cork would be one of the worst choices to build a structure with. Too many holes, even in premium quality. For the straight word, send in a FAQ.

Yeah, if you look in the right places you can find balsa that is the perfect density for wherever you may need it on your structure. Bass isn't necessary, but is prefered by some. Specialized Balsa has great wood for building your final structures before regionals and states, but any hobby store with a decent selection of wood will work fine for any prior structures.