The air volume is reduced by the glass sitting closer to the face and the overall design of the mask being smaller. Being smaller and closer to the face reduces the amount of air inside the mask, making it easier to clear since less air is used to clear and equalize. These last two points are the reason why in the early days they gained so much popularity among freedivers and spearfishers, requiring less air to clear and equalize, using less of that one precious breath. Some freedivers and spearfishers even used inserts or air reducers inside their masks to reduce the volume of air inside their mask, but nowadays they have many choices. The reduced air volume is not only the main advantage, but also where they get the popular name from. The Cressi Nano is a very popular mask amongst freedivers, not only because it is compact and comfortable, but it’s hydrodynamically designed, allowing them to glide through the water effortlessly.
There is also the Cressi Metis, which has a special edition lens, making it ideal for spearfishers and photographers, with yellow glasses that increase vibrancy of colors, also available with mirrored lenses that hide your eyes to the fish, adding to advantages of low volume.
Probably you are asking yourself, and why are they gaining popularity among scuba divers in general as well? Well, because there are more advantages, other than the reduced air volume, that makes them popular among all scuba divers, not only among freedivers and spearfishers. The reduced air volume is a huge advantage to scuba divers as well, but there are many more advantages. By the glass sitting closer to the face and exclusive inclined glasses on the Cressi Calibro for example, the field of vision is increased, allowing you to look down to check gauges or to even avoid the need of side windows. They are also smaller and lighter, making them popular for travel or pack in your gear bag, also they have softer smaller skirts that allow them to fit smaller faces, making low volume masks more comfortable, and even less drag. Another example is the Cressi Nano Crystal, which offers all the advantages of a low volume mask with it’s Crystal Silicone that offers incredible clear vision that helps prevent discoloration, reduces fogging and most important offers a Crystal view vision on a low volume mask.
Due to the advantages listed above, the low volume masks keep gaining popularity, and especially as there are more options of low volume masks, among all different underwater sports. The Cressi Z1, for example, offers low volume on a single lens design for a wide field of view for those who prefer single lens. So, there are a wide variety for different uses and preferences. But is low volume the best choice for everyone? Definitively not, some people get a claustrophobic sensation, for others the mask pushes against forehead or nose, or some people might not like the looks. But there are certainly benefits, aesthetically and functionally. Personally, I love my blue Cressi Calibro mask, which is an ultra-low volume mask with dual frame technology, giving me an amazing field of view, and I love the love the look of it
In summary it all comes to fit and personal preference, there is no right or wrong answer when it comes to low volume masks. Though they are certainly worth a try!