[richalex2010]

What type of epoxy is that, with what additives (if any)?
Looks like a "normal" epoxy (non-JB Weld) with chopped carbon fibre, or something similar.

A few other additives to think about for anyone using epoxies:
Kevlar
Fibreglass
Microballoons (microscopic glass spheres, looks like powder)
Colloidal Silica (rich man's microballoons, IIRC)

One material I've been trying to get my team to look at is a coupld of layers of fibreglass on each side of a sheet of balsa. Some of the strongest stuff I've used, probably on par or a bit weaker than G-10 sheet, and far lighter.

Composites are great, if used properly. A lot of the time they're overkill, though.