In reply to boulderholder:
Head height, got unlucky the way it landed I guess.
My current one, whilst it hasn't been properly dropped, has been blown along the base of crags by gusts of winds, been in my pack almost everyday (climbing instructor), I've banged my head in it plenty of times, been to various countries etc.
The lattice stuff has carbon rods in it and it has a layer of kevlar under the plastic shell so it is tougher than I at first appreciated.