Outer Shell: Selection of helmet protection is available -- fiberglass (bump only), ballistic protection V50 1400 fps and ballistic protection V50 2150 fps per MIL Standard 662, 17 grain fragmentation simulation. An outer shell is optional.

Inner Liner: An inner helmet liner attaches to both the outer helmet shell and communications system. and includes either an impact foam that is skived for ventilation or a high-moisture/high-humidity resistant ventilated foam pads. The liner is made of fire retardant Nomex®.

http://www.militaryphotos.net/forums/showthread.php?t=125663

http://www.gentexcorp.com/assets/gentex/Ground/DH132helmet.jpg