Check the viewing angle and fit. Many full-face masks use their one-piece design to ensure they have the broadest viewing angle possible, but everybody’s face is different, so peer out of the mask on land, if you can. Don’t forget to check the straps, as well. A firm fit is important, since if water leaks in, you’ll need to surface and remove the full mask. Make sure the straps are tight, but comfortable, and the mask is firm without being painful against your skin.