Most masks designed for scuba diving or snorkeling are made of soft silicone, which is hypoallergenic and resists deterioration. A double-flanged (two protrusions) face seal keeps the mask watertight. The pocket of air that the mask maintains around the diver’s eyes is important for vision because light behaves differently in water than in the air, distorting what you see. If the eyes were totally immersed in water, objects would appear larger and closer and that can hamper hand-eye coordination. A diver’s vision under these circumstances can be worse than legally blind.
