Self-Cleaning Glass 

Self-cleaning glass is glass that has been coated with a special dual-function layer that harnesses the elements windows and facades are exposed to -- namely, sun and rain -- to break down and wash away dirt. The first function is photo-catalytic; in other words, it is activated by light to break down the dirt that collects on it. The second function is to spread rain-water evenly over the glass. Most glass is hydrophobic (water-repellent), causing water to bead into droplets before it runs off, thus touching only a fraction of the surface. The hydrophilic self-cleaning coating prevents this beading into droplets, causing water to run across the entire surface, washing away the components that the dirt has been broken down into.