a quick plug for these footstraps -
these are kite straps that I recently bought and setup on my freestyle board.
They are made of 3 layers of EVA foam, with the highest density on the outer layer, and the inner layer comprising the softest foam which provides some cushioning.
The best thing about them is the EVA foam holds no water - so they weigh pretty much the same wet as dry. Dry weight is about 40 g per strap (on my dodgy kitchen scales - still extremely light). The standard straps they replaced weighed about 160 g dry, and something like 180-200 g wet, so these straps knock nearly half a kilo of the board weight.
I've had 3 sessions with them now, and am really happy with them. The weight difference is noticeable for me and they also have a bit of give which can potentially save an ankle or two. They look like they should last ok too.
google "nice x-light EVA strap" - they are only sold in sets of 2, but per strap are quite cheap I recon, so buying two sets is ok (have a spare strap if you only need 3).