I saw a demo where a guy sprayed ordinary shaving foam onto half a bathroom mirror, then wiped it off. When they left the shower on for a while, the treated side stayed clear while the other fogged up. Worth a try...
- S Richardson
Hydrophilic coatings.
Applying soap lowers the surface tension of water. Instead of "fog", which is comprised of tiny water droplets, you get the water to spread out into an even layer you can see thru. You also are eliminating some of the particles on the mirror that "catch" water droplets when you have freshly cleaned it off.
When scuba diving I have used anything from commercial anti-fog, baby shampoo, and even spit to clean and anti-fog the inside of my mask. They all worked as long as I didn't touch the inside of my mask after rinsing it. Touching the masks' interior deposits skin oils/particles and creates a space for the tiny droplets to stick, hence fog.
Some of the mirrors have a heating element in them.
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