While it is theoretically conceivable, we do not advocate it because a life vest is meant to keep your head above water, preventing drowning. If you wear a life jacket while snorkeling, you will always be struggling against it. The more resistant the jacket is to water, the more difficult it will be for you to move around. The main use for a diving mask is underwater vision. Without this feature, you would be unable to see what is happening under the surface or explore close-to-the-bottom. Diving masks are also used as escape equipment in case of air supply problems; they provide an alternative route for oxygen into your bloodstream in case the primary means of respiration fails. Finally, diving masks can be used as recreational gear by scuba enthusiasts; they allow you to see beneath the surface without getting wet. The principle behind a diving mask is simple: there is a rubber window mounted on a metal frame that fits over your face. The window is covered by a piece of glass or plastic that is held in place by two screws and one spring washer. When you put the mask on, the screws go through holes in the side of the mask and into your skull. This holds the mask tight against your face. There are several different types of diving masks, each with its own advantages and disadvantages.