If you ever intend getting on any government contracts, there are only certain types approved, namely:
B8.2.3.4.1 An aviator’s flight helmet, consisting of a one-piece hard shell made of polycarbonate, Kevlar, carbon
fiber, or fiberglass, must cover the top, sides (including the temple area and to below the ears), and the rear of the
head. The helmet shall be equipped with a chinstrap and appropriately adjusted for proper fit. Flight helmets for
helicopter usage must conform to a national certifying agency standard, such as DOT, Snell-95, SFI, or an
appropriate military standard, and be compatible with required avionics (see section B8.2.6.4.3). “Shorty” (David
Clark style) helmets are not approved. Flight helmets currently meeting this requirement are the SPH-3, SPH-4,
SPH-5, SPH-4B, SPH-8, HGU-56 and HGU-84. Helmets designed for use in fixed wing aircraft do not provide
adequate protection for helicopter occupants and are not approved for helicopter use.
Hope this helps......