The Mares HR Second Stage is a high-performance regulator with an engineered polymer body for ultra low weight. The HR second stage features a pneumatically assisted breathing design with cracking pressure adjustment knob for diver selectable breathing comfort and a large purge button. The Mares second stages also route part of the gas from the second stage valve directly to the mouthpiece through a bypass tube that creates a swirling effect or vortex movement. The core of the vortex is a low pressure area that pulls the diaphragm down during the inhalation phase, resulting in a markedly sensitive and easy breathing regulator. This Vortex Assisted Design (VAD) allows for the feel of natural breathing; you do not have the uncomfortable feeling of air being excessively “injected” into your mouth that is typical for high-performance venturi assisted second stages. The VAD also minimizes potential cold-water free-flow due to freezing because the gas expansion inside the 2nd stage occurs in the bypass tube, rather than on the mechanical parts.