>>537843
Basically this, the things barely provide more protection than just having a fucking skull. Hell, they basically need a spall liner just to protect from the fragments they produce in reaction to getting hit.
If you want fragment protection, I'd use some kind of the latest and greatest polyethylene with a kevlar liner, protecting the neck like >>537887 says. Lightweight, cheap, better protection, and no maintenance beyond keeping a layer of something to block the UV on the outside. If you design the helmet right, you could even add ceramic attachments to it at a later point to give minor protection from pistol rounds too.