FogCity® Fog Resistant insert lens is treated polyester film with a perimeter adhesive on the reverse side with a patented anti-fog coating on the top surface to prevent formation of fog. The anti-fog treatment is a patented polymer coating, which reduces fogging under normal temperature-humidity conditions (conditions with high humidity and extreme cold may cause frosting), even after repeated cleanings. The treatment is extremely hydrophilic which causes condensation to spread as a clear layer, rather than form droplets which appear as fog. Although it absorbs moisture, the coating does not dissolve in water, so it will not smudge when wet.