[Choven]

I've seen this done at science competitions. The box should hold small particles, like cat litter. The idea is that, when the egg hits it, the energy of the dropping egg is distributed across the surface of the egg that is in contact with the cat litter. Because the cat litter is somewhat light and small, high energy particles get shot out from the sides (think impact craters) taking some of the egg's energy with it.

You can try different materials (particle insulation?). I do know sand will not work. Good luck working on this