2 oz Sport bottle with carribeaner Mask Defog 500 PSI Mask Defog is without question the clearest, longest acting and most effective defog on the market. One application works for at least three dives in one day. Cleans your mask each time you use it. Wet or dry application. Divers will appreciate the convenient clip-on design which allows them to attach their mask defog to dive bags, duffel bags backpacks and many other items.