Good point. Take some serious lessons from the automotive industry and how they do impact attenuation. They've spent a LOT of money and man-hours solving many of the same problems you would otherwise have to figure out by yourself.If you want something that is nearly ideal, my suggestion would be one of the expanded metal foams that were developed for automotive bumpers. I've got a piece of it around here somewhere that was provided as a test sample and it's not appreciably heavier than polystyrene. It also will crush down to a much greater degree without any substantial rebound.
That's kinda why I'm planning on designing the cockpit and cabin first when I do get to actually doing serious engineering work on my concept. Plus, that way I have a complete structure that I can weigh and figure out just how much wing I need to build.It's one reason why it's so important to think of the cockpit as a system rather than viewing the components in isolation. The example I normally use to explain it to aviation folks is that you can't design the wings and tail independently because a change in one will dictate a change in another.