Abstract: An impact attenuating bladder for lining a helmet shell, the bladder having: a top layer and a bottom layer of fluid impermeable material defining a fluid containment chamber; a fluid outlet in flow communication with the fluid containment chamber; and a fluid release control valve in flow communication with the outlet, the control valve having: a sacrificial elastic membrane with an inside surface in flow communication with the fluid containment chamber and an outside surface, where the outside surface is disposed in an initial configuration when the bladder contains fluid at a minimum initial pressure, and in a rupture configuration when the bladder contains fluid at a maximum rupture pressure; and a membrane rupture device with a membrane engaging tip disposed a predetermined initial distance from the membrane in the initial configuration, and engaging the membrane in the rupture configuration.