What causes the "fogging" effect? Both atmospheric fog and "window" fog are made of tiny droplets of water, but they are not the same thing. In both cases, the tiny droplets scatter light in all directions rather than allowing light to pass straight through. Condensation forms because of a temperature difference between a surface and air.
The fog on the inside of a window is a comparatively small amount of water. An anti-fog coating causes the water to form a layer of water rather than droplets, resulting in a very thin layer of water that is easy to see through
A hydrophobic, or "water hating" surface, causes water to form droplets on the surface and easily leave the surface. A hydrophilic, or "water loving" surface, causes water to spread out and cover a surface rather than bead,
These types of surfaces are especially useful to avoid loss of visibility due to condensation. As we just discussed, water condensates on glass and causes it to become "foggy" because the tiny water droplets formed on the surface scatter light. When a hydrophilic anti-fog coating is applied to the glass, however, the condensation forms a thin, even layer of water instead of the droplets and the glass remains transparent.
Anti fog mechanism
Preventing condensation by increase wetting ability of the
Make the substrate “water-loving”
Increase surface energy
No water droplets formation
WCA < 5°