Types of Mask Lens
A single lens will offer one wide window of viewing for maximum visibility. In the past, single-window lenses were constructed in a way that the lens had to sit further from the face, making it more difficult to equalize pressure. These days, almost all masks are constructed with a low volume for easy mask clearing and pressure release. If needed, there are prescription lens inserts available for this type of mask.
In general, a dual lens mask offers a lower volume, making it easier to clear and equalize pressure. The dual lens style mask design allows the lens to be closer to the eye. Most lenses on this style mask are made in a teardrop shape that’s wide at the top and narrow at the bottom. This offers a wide view in the main line of site, while still offering a nice downward view to look at your watch, gear, etc. A lot of dual lens masks have prescription lens replacements available, so be sure to ask a salesperson if this is something you require.
There are more options than just single or double lens masks! There are triple and even quadruple lens masks available. These styles will have either a single or double window style in the front with an additional window on each side. These side windows not only allow for optimal peripheral vision, but they also allow more light into your mask. They are a great option for those who get claustrophobic.
Double Edge Skirt
While the silicone style skirt seals to the face, this style skirt has an additional layer on the inner side of the skirt that covers more surface area, creating a much better seal and causing less leaking.
Mask Purge Valve
While not as common, the purge valve on a mask allows a snorkeler to exhale water through a 1-way valve in the nose section in the mask while the head is under the water, versus needing to lift your head upright so that gravity forces the water out the bottom of your mask.