This is the Ocean Reef ARIA - Full Face Snorkeling Mask Features: Full Face Mask Design Built-in Snorkel with Dry Top System Wide field of view Crystal Clear Vision ARIA. A full-face snorkeling mask with a wide field of view for shallow freedives and surface snorkeling. Aria allows divers to breathe through their nose, while the dry top" prevents water from getting into the snorkel. The Aria sports the largest field of vision of any snorkel mask around. Inside the mask frame, the breathing circulation guarantees no fogging and no extra stress. The Aria reduces jaw fatigue, eliminates the possibility of water getting into your snorkel, improves your ability to breathe easily and gives users a field of vision seldom seen in the industry. To determine size, measure from the bridge (top) of your nose to the bottom of your chin. Greater than 4.5 inches (11.5cm) will be size L/XL. Less than 4.5 inches (11.5cm) will be size SM/MD.