simon - what type of toothpaste are you using? Make sure you use the paste type and not the gel type. Rub it in, let it sit over night, and then rinse it. You may need to do this a few times initially. The toothpaste is to get off the initial manufacturing residue. You only need to do this with new mask. Afterward, use a commerical defrogger or spit before each dive. If you want, you can also use a diluted solution of baby shampoo. Rub some on the inside of the mask, and then rinse it out.