Patented dry top prevents water from entering at the surface or underwater A self-draining purge valve at the bottom allows water to exit A reservoir at the lower end allows you to breathe past small amounts of residual water The comfy mouthpiece uses a unique bridge that runs behind your front teeth to hold it firmly in place. This avoids clenching and allows you to relax your jaw. The mouthpiece is replaceable and can be changed out for a smaller model or a more traditional model The Passage snorkel represents the latest in snorkel dry top technology. This highly efficient dry top, coupled with a self-draining lower end, results in an easy and comfortable snorkeling experience.