Condensation occurs on the inside of your mask lens when diving, if not treated with a defog solution this condensation will create a mist like you see on the bathroom mirror after a shower. This layer of water makes looking through the mask lens impossible. Proper defogging of your dive mask lenses is vital to an enjoyable dive. Using a defogger from a company that has built its reputation on diver's optics is a no brainer. Use only the best from Sea Vision. Seavision's Defogger comes in a handy 2 oz. spray bottle. Just a small amount sprayed on your mask lenses will keep them clear through out your dive.