Use EVA-foam.Its also used for many mose-pads.

If you want to build a lighter plywood board look at http://www.stuntkites.nl/kiteboards/vaasboards.faasboard5bouw.html It gives the description for a 4 layer of 3.6 mm Ocumé plywood. Because the 2 middle layers are cut out you can bring down the weight. I have built 3 of these boards and they su...

Sorry,
http://www.stuntkites.nl

Go to http://www.stunkites.nl for the description of the servaas 5. Just look at the way of building and develop your own board. But I broke already 2 of these boards after a jump. But this will only give problems for the heavyweight kiteboarders (95 kg +) or you have to respect your board and only ...