Originally Posted by FBinNY

Think about cars for a moment, and why you wear seatbelts. Without them, the car crashes and slows as it crumples. meanwhile, you continue until you hit the now slower moving car and smash your face. The seatbelts protect you by making you part of the car. Now imagine how much better you'd do if the entire car was filled with foam so there was absolutely no room to move. Now you get the full measure of protection the car can offer, and the impacts are spread evenly over your entire body.