A dive buddy of mine brought a bottle of this on our last trip to the lake, and I figured I might as well try it out. What a giant waste of money! I can't believe anybody would seriously pay for this stuff. Yes, it will help to defog your mask for a little while. But after not more than 20 minutes in the water, mine was fogging up like crazy again. Maybe if you are looking for something in more of a snorkeling context, this would work for you -- but it's an awfully disappointing scuba dive that only lasts for 20 minutes. Here are some tips if you don't want to go out and wate your money on stuff like this: When you get a new mask, use toothpaste to clean out the inside (it must be the paste and not the gel, because it needs to have that extra abrasive edge). From then on, you can use baby shampoo. It will work better than this and I'll bet it's cheaper too!