POWERBREATHER Sport Fresh air: oxygen flows in the top & Co2 expels out the bottom No gurgling: no water comes in the top vents, only air, due to Powerbreather innovative Membrane technology Sport PB0100 not Intended for flip turns in pool or choppy open. See lap or wave editions US at (Triathlon) legal (unless otherwise deemed by race director) Open water swimming for freestyle, breast, butterfly and side stroke Leaks in seal to your face effect breathing Diving down is challenging with the air filled mask. Can not equalize by holding your nose when diving deeper. Difficult to remove in a hurry. CO2 mixed air danger!