Anti-fogging – why do sunglasses fog up and what are the solutions.
Fogging is caused by a “phase change” of water vapour to liquid. This occurs almost exclusively when warmer air meets a cooler surface. So if you use your LiP Watershades in a cold water environment, read on…this advice is for you!
For watersports sunglasses, the main cause of fogging is when warm air from your body or your breath comes into contact with lenses that have been cooled down (either by the air temperature or by the water temperature). The water vapour in the warmer air condenses into tiny droplets that cling to both the inside and outside of the lenses.
For fogging to develop, the temperature of the lens surface must be below the ‘dew point’. The dew point is the temperature at which air must be cooled to become fully saturated with water vapor. If in the example above the lens temperature is above the dew point, then fogging is unlikely to occur. Fogging is also extremely unlikely to occur when cold air meets a cold surface, or where warm air meets a warm surface or indeed when cold air meets a warm surface. The problem is worse on cool damp days when the dew point is lower.
A classic scenario when fogging can develop is when a kitesurfer suffers a wipe-out and loses their board inside a wave set. As the waves crash over you while you work to retrieve your board, the temperature of your lenses will drop to meet the surrounding water temperature. As you exit the water and start riding again, the warmer air may suddenly condense and your lenses instantly fog up. This is further exacerbated by heavy breathing. The fogging that develops will remain until the temperature of the lenses equalises with the surrounding air temperature.
What are the solutions?
Given that the laws of nature determine if and to what extent fogging occurs, the question is not how we can prevent fogging from happening in the first place, but rather to present solutions for when it does occur. Some manufacturers use so-called “anti-fog coatings”. The truth is that these coatings have a tendency to degrade very quickly, and because the anti-fog coating is generally soft and pliable, they can easily scratch too. So, this is not a good solution.
Here at LiP, we have addressed fogging by a combination of innovative product design and just as importantly, recommending suitable user habits and routine product care.
- Our patented double vortex vent system encourages air flow behind the lenses to clear fogging from the inside. Get moving again, and the fog should clear.
- Hydrophobic lens coatings that repel moisture. Water on the lens surface is encouraged to “bead” and slide off the lenses.
User behaviour and Product Care tips:
- The fog should disappear once you are moving again and the double vortex vent system is allowed to do its job. If the fogging is 100% and you cannot see anything through the lenses, release the leash clasp a little and hang them around your neck to allow more airflow across the lenses until they are clear again.
- Avoid touching or wiping the lenses when they are wet or fogged up. Wiping the lenses when they are wet will only disrupt the hydrophobic surface and encourage water to accumulate where the lenses have been wiped.
- Avoid placing sunglasses on top of your head. Heat and sweat from your head (the hottest part of your body) will accumulate on the inside of the lenses.
- Take care of your Watershades after every session on the water, and be sure to let them dry before you buff them with the microfibre bag. Particles on the lens surface will attract water and dirt, so check for dust or marks on the lenses immediately before you head out on the water. See our product care guidance for more details – https://www.lip-sunglasses.com/2017/12/07/taking-care-of-your-watershades/