Blonde Girl With A Diving Mask In The Sea

Sometimes masks are sold in conjunction with snorkels and/or swimfins. Low quality snorkelling masks may have a low-quality plastic or glass faceplate, and are not recommended for anything but rare, casual use. Masks that have the snorkel built in are considered hazardous as well.
Divers often test whether a mask is a good fit by placing it on their face, without using the straps, and gently inhaling through their nose. If the mask stays on without any help this indicates that no air is being drawn in and that the fit is good.