He says "balsa" for the wings but it looks to be a plywood - not balsa.
Balsa is very light in colour and VERY light in weight with very fine grain. Also, it's VERY fragile and hard to get in large sheets like that (most of the time it is in little 'strips'). I would not use balsa for the wings. They'll just break off on you.
From the pictures it looks to be a 1/8th inch think piece of plywood with grain that is not very fine.