This is the Apeks XL4 Scuba Diving Regulator Features:1st Stage: Breakthrough, innovative over-moulded first-stage endcap and environmental diaphragm help prevent ice build-up that can cause first stage free flow in extreme circumstances. Also protects the first stage from impact damage Large surface area heat exchanger diaphragm clamp helps increase the gas temperature inside the 1st stage, resulting in improved cold water performance Unique over-balanced diaphragm design-as the diver descends, the over-balancing feature allows the medium pressure gas in the hose to increase at a faster rate than ambient. This results in superior performance at depth Compact machined 1st stage based on the expedition tested Apeks DS4 platform. 2nd Stage: Compact and lightweight 2nd stage improves comfort and helps reduce jaw fatigue on long duration dives High-performance, pneumatically-balanced, lever-operated poppet valve Large, over-moulded, self-flushing and controllable purge button Ergonomic Venturi lever is easy to use and locate Flexible nylon braided hose has better cold water performance than traditional rubber hose Standard metallic hose connection for interchangeability Comfo-bite™ mouthpiece has a unique bridge that fits across the upper palate and does not require bite pressure to stay in place Re-useable mouthpiece clip makes it simple to change mouthpieces in the field Durable and flexible rubber exhaust tee provides excellent bubble diversion. The Apeks XL4 is especially well-suited for the technical exploration diver who prefers cold water climates. Compact and lightweight, it helps reduce jaw fatigue during long, cold dives. Designed with an innovative, over-moulded endcap in conjunction with the environmental diaphragm that helps prevent ice build-up. The XL4 makes an ideal stage regulator and is also an excellent high-performance option for the technical exploration diver who is serious about maximizing functionality and minimizing weight.