I had originality planned to make the Whirlygig-38's fins from some 4 1/2 inch wide, 1/4" thick wood that I liberated from the Habitat for Humanity ReStore. Upon closer inspection, I found this is not plywood. I'm not exactly sure what it is, but I don't trust it for the big 'Gig. I'm leaning toward a passive, autorotative recovery scheme and the fins will have to be sturdy.
I also considered 0.093" Lexan. Lexan is tough an may handle a secondary impact after initial impact, but I don't know about the floppyness during boost.
So, I decided to use 4" x 12" x 1/4" plywood planks from Michaels. These will provide enough area and being pre-cut appeals to my laziness.
I'll be working on the 'Gig some time today.