National Geographic's Z-9 swim mask incorporates the best features of both snorkeling masks and goggles to give maximum comfort and true seal reliability. The single construction skirt adds to the comfort by evenly spreading the sealing pressure over the forehead and cheekbones. The replaceable silicone mask strap can be easily adjusted using the same ratchet quick lock design found in the Nat Geo Snorkeler Mask Series, with a simple pull to tighten or a press of a button to release. The ergonomic design allows for a 180° view with minimal distortion and scratch-resistant UV and anti-fog protection help keep the view clear.