500 PSI Mask Scrub is specially formulated to clean new and old mask lens prior to defogging. 500 PSI Mask scrub gently removes mold release found on new masks that can prevent defogging. Periodically use Mask scrub to remove residue buildup on older masks. Just apply a liberal amount to the dry interior lens surface and rub in firmly using your fingers, then just rinse in fresh water to clean.