Diving Masks

The diving mask is an item of diving equipment that allows scuba divers to see clearly underwater. While the diver’s eye is in direct contact with water, light entering the eye is refracted by a different angle and the eye is unable to focus the light. By providing an air space in front of the eyes, light enters normally and the eye is able to focus correctly.
Diving masks have a durable, glass plate in front of the eyes and a "skirt" of rubber or silicone to create a watertight seal with the diver's face. A strap keeps the mask in position.

Divers often test whether a mask is a good fit by placing it on their face, without using the straps, and gently inhaling through their nose. If the mask stays on without any help, and air doesn't get in, then the fit is good.