The Carbon formers are actually balsa with .007 carbon fiber accent panel laminated to them. It looks cool, doesn't add much weight, and most importantly, it stiffens the wing area formers like steel. It ain't cheap though. But it works a lot better than straight balsa or ply. You have to be very careful though, because one stray drop of glue, or too much CA around it will make it look awful and you'll never get it cleaned up. When I glue them in, I use electrical tape over them to protect them, which doesn't come off until after it's painted. Then it makes me look like a better, cleaner builder than I actually am =)

-Mike