Originally Posted by jgiddyup
I'm honestly asking this question because of a lack of understanding. How is it possible for sunglasses to fog or have vents? Even if they're wraps, they're still fully exposed to the elements and will acclimatize in a minute or so.
It depends on how they fit your face. If there's a pocket of low airflow next to a highly sweaty skin patch. . .
For example, mine tend to fog because I take a large lens for a wide face, and that usually means the upper edge overlaps the upper orbit/eyebrow area, so any sweat vapor off there creates instafog on the cold lens.
I usually don't get any fogging from perspivapor around the nose, but I know people who do.
The idea is to get a continuous, well-distributed but slow airflow over the entire lens without irritating the eyeball.