Almost all scuba diving gear requires some preparation before it can be used. When you bring home your scuba mask, you will notice an oily film on the lens of your mask and sometimes on the strap of your mask.
Most manufacturers rub a light oil onto the silicone to help protect it during shipping. You need to remove this film before you use your scuba mask, otherwise your mask will continually fog while diving. An oily film on your mask will prevent it from sealing properly, or the mask may slip off your face during a dive.
To clean your scuba mask, apply a pea-sized drop of toothpaste, not gel, to the inside of the lens. Using your fingertips rub the toothpaste in a circular motion around the entire surface of the lens. Do not use your fingernails; this may scratch the lens of the mask. Rinse with clean water and repeat until the film is completely removed. You can also rub toothpaste up and down the strap to remove any film.
Always rinse your mask thoroughly after cleaning.