Fogging is another nuisance during scuba diving. No matter what mask you use you will most likely experience it during some of your dives. The principles are similar to what happens if you wear glasses outside in the cold and you enter a warm room. They instantly fog up. The same occurs underwater when you transition between different temperature layers. There are some possibilities to prevent it though. First, prepare your new mask as we have mentioned above. Use toothpaste to clean out the mask and then rinse with warm water. After that use defogging spray every time you go scuba diving. That should usually help you avoid that your mask gets foggy during a dive.