Let's offroad / mountain bike / mtb / ride dirt

MTB helmets in general are just styled differently (peaks) to road helmets unless you go for a skate lid style one. There is a giro hex helmet which has a little more protection around the back of the head than a road helmet. A few others like this too. I know I've just contradicted myself.

I just bought myself a new lid a few weeks back. Talking with the guy in the shop, the only difference between road and off-road designs is the shape of the back. Road ones tend to go for a more aero form but off-road ones are straight protection. Of course you then get the extreme stuff like super aero track helmets, full face downhill ones, etc. But for standard issue kit, the back of the head trade-off seems to be all there is. Certainly the basic construction and level of impact resistance are identical.