Scrubbing the inside of the lenses with a non-abrasive material (toothpastes work well) is vital on a lot of masks, but as indicated already be careful as to if it has oem fog retardant on the lenses. Smokers will have more problems than non-smokers because smoke is retained in the lungs and will leave a film on the lens due to equalizing/clearing the mask.
1. Sea Drops - this is a diluted defog that is just thicker than water and works well for masks that are well broken-in.
2. Sea Gold - this is a thicker gel-type defog that is stronger than the Sea Drops and works well as a general purpose defog.
3. PSI 500 - this is a thicker gel-type defog that is considered "heavy duty" and works well for problem foggers because of the difficulty of washing it off.
Some important factors to remember with defog are:
Don`t apply/rinse your defog until you`re ready to enter. Make this your last step before putting on your mask.
Do not let your mask set in direct sunlight for any length of time more than 1-2 minutes. The tempered glass will cause heat to be trapped between the mask and your face which causes the outside of the lens to be a different temp than the inside - result is fogging.
Wear quality sunblock, especially around the area your mask will be. The sunblock will help keep the temperature down on the surface of your skin where your mask will be. This also helps equalize the temperature of the lens, lessening fogging problems.
Rinse your mask thoroughly with fresh water after use. It helps eliminate contaminants that aid to fogging problems. Your other gear should be rinsed anyway, so why not your mask too?
Follow the directions for use. The directions are there because the process has been tested and proven to work.
When in doubt, whip the "spit" out. Spitting in your mask is not always a bad idea, but you should remember that saliva has corrosive enzymes that can leave a residue on your mask after extensive anti-fog spitting.
Air dry your mask (or any gear for that matter) before you store it for ANY length of time, no matter how short.