The snorkeler can orally inflate and deflate the volume of air in the vest to their requirements. Add just a little air to use it as a "pillow" under your chest to help hold your head and snorkel above water. Fully inflate in stressful situations to relax and rest. Deflate by yourself to return to surface diving activities. Fits comfortably over the snorkelers head and secures firmly to the body with two adjustable straps.