Where I work we have this non-flexible polymer composite called synthane and it comes in 4X8X3/4 sheets. Now I was wondering if this woould work for a box? I mean in theory it should, its dense and non flexible. I was just wondering if anyone has ever head of this material. I highly doubt its ever been used as in a box, I would imagine its very expensive.

Don't see why not. I don't think it would have the greatest damping characteristics, but who knows. It's worth a shot if it's cheap enough. Your main question will be, how easy is it to tool.