Originally Posted by Allister
Next would be the crushable layer where the real work is done. I'd look at using a closed cell foam (a product called Sorbothene is what I've been considering). Without doing any sort of testing or calculations, my suspicion is that this layer could be thinner than the layer of styrofoam currently employed and provide as much or more capacity to decelerate the skull.
While we're at it, I'd like to see the coverage extended to include the back of the neck and possibly the ears, but allowing for the range of movement that occurs in normal cycling.
Discuss.
So basically you're designing a helmet with a bit more "crash comfort" that still destructively dissipates energy, meaning it will self destruct on impact like other helmets except this will "look" like it self destructs in a better way than just cracking.
Most helmets already provide protection in that matter since the mass sticks out beyond the ears and back of the head. Anyway you put it, I still dont think you're gonna find any type of material that will provide crash protection up to the point where, the impact forces inflicted at the neck take over in something that weighs as little as the current helmets on the market.
If you want inspiration, look into motorcycle and motorsport racing helmets. Only keep in mind that they're designed for different crash kinematics and geometries.