Chris writes "Consumers across Europe can now purchase self-cleaning glass that promises to keep windows free from dirt. The key to Activ glass is an ultra-thin coating only 40nm thick applied to the glass surface during the manufacturing process. The coating, which is based on titanium dioxide, works by combining the two beneficial effects. First, the ultraviolet wavelengths in sunlight react with a photocatalyst to break down organic debris on the glass. The second feature is that the coating is hydrophilic, meaning that when rain hits the glass, it doesn't form droplets. Rain water flows down the glass in a sheet and washes the dirt away."