Foggy lenses is an eternal dilemma for every glasses wearer. But it isn’t specific to them alone, as foggy windscreens on a cold rainy day are equally exasperating. The “fog” is the result of a relatively significant discrepancy between the outside temperature and the temperature of the lens. The hotter surface of the lens tries to give off heat out to the cold, and in that attempt, the energy within the gaseous water molecules on the lens decreases causing them to condense and form “fog.”
So how can we stop the fog from forming? As the video below elaborates, there are two primary types of substances that can help, namely surfactants and hydrophilic ingredients.
Surfactants include everything from human saliva to baby shampoo and emulsifiers, which work by lowering the surface tension of water. Since the water droplets’ surface tension is reduced, they can’t keep their shape and turn in a very thin film of water that doesn’t interfere with your vision. Almost every anti-fog spray uses this phenomenon.
The other primary way to prevent the annoying fog from building up is to cover the lens with a hydrophilic coating, which includes polyvinyl alcohol, polymers, hydrogels, and colloids. These hydrophilic materials absorb the water and thus prevent the droplets from turning into visible “fog.”