Diving masks may have a single, durable, tempered glass plate in front of the eyes and a "skirt" of rubber or silicone to create a watertight seal with the diver's face.Some masks may have two lenses, which in some cases allows the user to fit prescription lenses. In the case of freediving masks, which need to be low volume to minimise the change of pressure that occurs with depth, the lenses may be made of polycarbonate plastic. All masks have an elastic strap to keep them in position.China's processing diving mask
Masks that are used at depth must be constructed so that the diver can exhale through the nose into the mask to prevent the "squeeze" caused by increasing pressure during descent in water.China's processing diving mask The nose section of the mask also needs to be flexible to allow the diver to perform an eqalisation maneuver such as the valsalva maneuver or the frenzel maneuver when equalising pressure in the middle ear.
China's processing diving mask----To prevent a mask from fogging up due to condensation on the glass plate many divers spit into the mask, wipe the spit around the inside of the plate and wash it out with a little water. There are commercial products that can be used as an alternative to the saliva method.
