Why lenses mist up and how to solve the problem

11th October 2016

Why do lenses mist up? Fogging happens because of the so called ‘phase change of matter’.  Water vapour (from exhaled breath and sweat from your forehead) cools down when it comes into contact with the lenses. The cold lenses cause a phase change as the warm vapor surrounds the lenses and turns the air into a liquid. Fogging also occurs when the lens is colder than the air surrounding the lens. That often happens if you move from outdoors to the indoors. Or if you take your eyewear out of the relative warmth of a kitbag in cold air. A more technical explanation (should you be interested!) is that when the air near the lens is cooled by the lens, the relative humidity of the surrounding air will quickly increase.  As air cools it looses it’s ability to carry water vapour. Once the relative humidity reaches near 100%, water will begin to collect on the lens. Even in fairly dry air, if the temperature difference is great enough you will get lens fogging.

Fortunately there are now some really good anti-fog remedies available, many specifically designed for close fitting sports sunglasses and ski goggles. We now have several options in our accessories section including a new addition of anti fog wipes.