If you’re familiar with newer car models, you’ll know that when the rear windshield fogs up, pressing a button slightly heats up the glass and removes the fog. There are no eyeglass frames that do that yet but there are anti fog eyewear that never fog regardless of weather condition. Especially in what we can observe in this season’s ever changing weather (turning from cool and wet to suddenly hot and sunny), having your eyewear fog up might happen more commonly than you think.
The anti-fog component in an eyewear is actually found in the lens themselves. What gives a pair of glasses anti-fog properties is the anti-fog coating that is applied on the lenses. There are anti-fog solutions that can be applied as a spray (for windshields, industrial equipment, etc.) but you can’t be reapplying anti-fog spray every 8-12 hours. For glasses as well as safety goggles, it’s common that the lenses are dip coated. In turn, your eyeglasses frames could accrue fog but never on your lenses.
This is the most commonly used coating for anti-fogging lenses. Hydrophilic (water loving) agents make sure that water is spread as much as possible on any given surface. This means that, in the instance of the formation of fog, instead of the surface collecting small particles of water on the surface, it disperses the particles throughout the lens so that you’re seeing through a clear layer of water instead of small blotting particles of moisture.
As opposed to hydrophilic agents, hydrophobic coating does exactly what you think: it repels water. It seems to make sense that coating lenses with hydrophobic solutions are much better but because hydrophobic solutions take no other form, we’re back to why we use hydrophilic films instead of a coating spray: solutions need to be reapplied to surfaces constantly. But it still is a pretty cool process to look at though.
We’re still a long way to go from looking at eyeglasses frames doing the anti-fogging for us but with these solutions available, it seems that we’ve come to a visual breakthrough when it comes to line-of-sight safety.