|1. A protective helmet, comprising:
a hard plastic shell having a front, opposing sides, and a rear, and a hole there through at said rear adapted to be positioned
proximate an occipital bone of a wearer; and
an internal inflatable rubber bladder comprising an elongate rubber tube having a length and a constant circular cross-section
along its entire length with constant diameter within a range of between 1.95-2.25″, sealed at opposing ends, and a valve
equidistant from said opposing ends, the inflatable rubber bladder being configured inside said hard plastic shell with equal-length
branches defining two identical diametric lobes on said opposing sides of said hard plastic shell and joined together at said
rear, said valve being mounted in the hole of said hard plastic shell.