The best way to stop your mask fogging is to give the inside glass area a scrub with a mild abrasive paste.
Many commercial products are available but we have found the best is a home-made one made up of toothpaste and detergent.
The toothpaste acts as a mild abrasive while the detergent helps to lift the release agent off the glass. Some minor scratching may occur when you scrub the glass, this should not cause any problems while in use.
We suggest you anti-fog treat your mask in the evening over a few advert breaks while watching TV, massage the mixture into the inside of the mask lens. Avoid any side windows it they are acrylic as they will scratch badly. After about 6 advert breaks, leave the mask and let it sit overnight. In the morning wipe the dried paste out with a dry cloth and then thoroughly rinse the mask in water to remove all traces of the paste. The mask lens should now be 'squeaky clean' on the inside surface.
Before you enter the water, while the mask is still dry, you will need to spit into the mask, wipe it around and then rinse it out.
Once your mask has been treated with the anti-fog scrub it should not require treatment again.
If spitting is not your style then commercial anti-fogs are available for around $1.00-$20.00 a bottle. Most commercial anti-fogs will need to be re-applied before each use.
Or you could spend $22.00 and buy some of the latest technology TUSA Freedom Film......