Here is the offal of my dissected hat and you may be able to see that the polystyrene on the left hand side (shown nearest in top photo) where I hit my head has before deformed due to the impact causing the polystyrene cells to compact. So, it has done just what it was designed to do but can only do it once. That's why you should throw them away every time your hat comes into contact with the ground as a result of a fall or being dropped. There is no sign of any damage on the exterior surface of the hat itself. (And a good excuse to go shopping eh?)
