Promate mk600 Adult Stealth Snorkel Scuba Dive Mask, Black Flexible silicone for leak-proof, comfortable fit and Watertight Seal Tempered-glass lens for safety: forget flimsy plastic lenses! this one is quality tempered glass, which resists scratching and shattering Convenient buckle for easy adjustment: simply pull the straps to desired fit and the buckle will hold the straps securely in place. Presto: customized comfort