It increases breathing security and provides a space for equipment that lets the diver communicate with the surface support team.

[2] The full-face mask provides breathing gas to the diver, and an air space to facilitate underwater vision.

[3][4] For some applications it is desirable for the gas inside the mask or helmet to remain at a pressure slightly above ambient at all times while in the water, as this will prevent any contamination from leaking into the gas space during inhalation if the face or neck seal, or the exhaust valve system, does not seal perfectly.

Additional components may include communications equipment, lights, alternative breathing gas connections, and a means to defog the interior surface of the faceplate.

[2] Two basic configurations are in common use: Those with a soft elastomer skirt which seals around the periphery of the face, and those with a rigid frame supporting the other components, which is sealed to the face by a soft foam ring which is clamped to the frame by a metal band, to which the straps are secured (band mask)[citation needed] The faceplate, viewport, or lens is a transparent window, usually flat, which encloses an air space in front of the diver's eyes and allows the eyes to focus correctly underwater.

The rubber moulding which incorporates the skirt seal may also be sufficiently stiff in places to partially perform this function (Cressi-sub, Scubapro), and the faceplate may also be structural (Dräger Panorama, Ocean Reef Neptune, Aga Divator).

The frame supporting the functional components must be sealed around the face to maintain a leak free internal air space over the eyes, nose, and mouth.

[2] A band-mask is a type of full-face diving mask with a rigid and relatively heavy frame, to which a face seal is clamped by a metal band.

Band-masks generally have a single faceplate, which may be relatively large, firmly mounted to a rigid frame which also holds the demand valve or other gas supply components.

A face seal, and in some cases a neoprene hood, is clamped onto the edge of the frame by the metal band which gives the mask configuration its name.

It is usually a rubber component comprising a group of straps radiating from a central patch or ring, which rests against the back of the diver's head, low enough to resist slipping off over the top.

This allows communications equipment (usually an intercom wire or by modulated ultrasound) to be installed in the mask and is very useful for working divers.

[citation needed] If an open plan full-face mask floods underwater, it can be more difficult to clear than with a mouthpiece.

[2] A mouthpiece with bite-grip connects the gas supply directly to the diver's mouth inside the mask.

This feature makes it possible to use bailout gas supplied by a dive buddy with a standard regulator while wearing a Supermask.

[11][2] Demand valve, twin hoses, rebreather mouthpiece or free-flow air supply hose may connect to the mask in various ways, including:- The full-face mask is generally the last piece of equipment fitted before the dive, as it is cumbersome and makes fitting other equipment more difficult by restricting the diver's field of vision, and the mobility of the head.

The straps must be tensioned sufficiently to ensure a good seal, and to hold the mask securely to the diver's head, but not so tight as to cause discomfort during the dive.

[2] Most full-face masks do not have fresh airflow directly over the interior of the faceplate, and are to some extent susceptible to fogging by condensation during a dive.

[12][2] Full-face masks intended for use with scuba may provide a method of switching to atmospheric air when above the surface, to save breathing gas.

Rebreather systems often incorporate a dive/surface valve in the mouthpiece which may provide an opening to the ambient environment when the loop is isolated.

[citation needed] A full-face mask provides better security of breathing gas supply than a half-mask if there is a risk of the diver losing consciousness underwater.

[2] The mask faceplate is generally a high impact strength polymer which is securely attached to the skirt or frame.

A major flood caused by a temporarily dislodged mask is easily drained by purging after replacing it in the correct position, and adjusting the straps if necessary.