Scuba and snorkelling masks, sometimes called half masks (as against a full-face mask) have either a single or a double lens to look through. The glass is tempered glass able to stand the pressure of diving without shattering. The lenses are held by either a hard plastic frame or they may be frameless in which case the glass is bonded to the flexible silicon of the mask.
The skirt of the mask has it’s own seal as that is the portion designed to seal on the face. The skirt also has a nose pocket moulded into it to assist the diver in equalising pressure between the middle ear and the surrounding or ambient water pressure. The skirt material could be rubber or the more flexible silicon. Rubber degrades faster in sunlight than silicon and does not have as effective a seal on the face. Rubber is usually black but the silicon material might be either black or clear. Clear silicon allows more light in (and distractions) and is often preferred by newer divers. Black silicon is often preferred by snorkelers, free-divers, and technical divers as it reduces distractions and allows for greater focus of concentration.
Some masks have a one-way purge valve built into the frame. Newer divers who have difficulty removing (clearing) water from the mask may prefer this style. Some Scuba masks are quite large and therefore have a large internal volume that has to be equalised during descent. Snorkelers only have one breathe for their dive and don’t want to waste air adjusting the mask volume during descent. Snorkelers therefore prefer a low volume mask.
There is a mask strap which keeps the mask in place on the divers face. This strap must be positioned at right angles to the mask glass for maximum comfort and best fit. Most straps are split, or wider, at the back of the head to assist in correct mask placement.
A guideline for selection might be: New recreational divers – clear silicon mask with a purge or no-purge. Experienced recreational diver and technical diver – black silicon non-purge mask. Free-divers and re-breather divers – low volume black silicon non-purge mask.
Watch for part 2 of this blog which covers fitting your mask. For further information or assistance call in to talk to NZ Sea Adventures staff, 9 Marina View, Mana.