US Patent 9119433 Helmet system

A protective helmet for successive impacts includes a head cap adapted to surround and move with a wearer's head and an outer shell which surrounds the head cap. An energy absorbing flexible liner predominantly comprised of radially oriented foam columns is attached to both the head cap and outer shell. The liner establishes a preset initial relative position and spacing between the head cap and the outer shell and compliantly absorbs energy imparted to the outer shell during a helmet impact to enable the outer shell to move linearly and angularly relative to the head cap during the helmet impact and to be returned to the initial relative position with the head cap following the impact.