What causes mask fog (and how to stop it)?

[cneal]

I use baby shanpoo or spit when I forget the shampoo. Fog is condensation. I have found rinsing with a splash cold water will help.

 

[Storker]

At certain conditions, fog is inevitable. Warm, moist air against a cold glass surface is a failproof recipe for condensation. You can't beat physics. Or is it chemistry?

Defog works by being a surfactant and preventing tiny droplets forming on the surface, but instead making the condensation form a film on the mask glass. If conditions are decent, my spit works well enough as defog, at least if I've prepped my mask properly. So I've never bothered to research commercial solutions since spit is free and always available. If my mask should start fogging up while underwater, I let in a couple of tablespoons of water, look down, turn my head both sides and then clear my mask. Problem solved.

 

[tcphil]

All of the defogging advice is good. Would also recommend you think about your technique. Some newer divers have a tendency to regularly exhale out of their mouths, with just a little out of their noses also. When helping out in pool sessions and I see someone fogged more than others, I look for this as one way to help correct.

 

[DogDiver]

Stop exhaling inadvertently through your nose.

 

[Antmany2k]

i usually toothpaste it on the night before the dive and then spit and rinse before a dive. give it a good old spit and its clean as a whistle, as my instructor told me "the greener the cleaner"

 

[Alastor]

Where do you store the "old" spit ?
Also, exhaling inadvertently through the nose can accelerate the fogging process, while exhaling consciously would not !

 

[icechip]

+1 on the baby shampoo. It's cheap, easy and smells nice. I have one of those travel tubes full of it, put a little splotch on each lens while I'm gearing up. A quick rinse in the ocean water and it is good to go. Have not had fog issues since.

 

[Buliwyf]

Dawn Powerclean at the hotel. Seagold Gel at the dive sight.

That seems to work best for me. I do exhale out my nose often to push water out of my mask or squeeze, or cause I flooded my mask to clear a spot.

 

[Charles2]

Along with a good spit cleaning, I have found that if I remove my mask after entry and allow the water to cool my face to water temperature any fog is almost gone for the entire dive. This is especially true if the water temperature is lower than about 72º F.

 

[Storker]

I remove my mask after entry and allow the water to cool my face to water temperature any fog is almost gone for the entire dive.

In cold water diving, this is (IMO) sound practice. Losing your mask, or having a major mask leak can be shocking if the water is cold. Dipping your face in the (cold) water before starting the dive prepares you for the shock of cold water hitting your face and reduces the risk of freaking out you lose your mask during the dive. Less risk of freaking out.