Water cannot spread out on these leaves so it rolls around as droplets, removing dirt and grime as it goes. The new technology might stop problematic water films building up on flat surfaces. Lotus leaves' water-repellency depends as much on the bumpy leaf surface as on its waxy coating. Roughness reduces the ability of water to spread out, so droplets snag and gather up into almost spherical beads. The lower the contact angle, the more the liquid spreads over the solid.
Complete wetting occurs at zero degrees.
Artificial hydrophobic surfaces must have contact angles greater than 150 degrees to earn a 'super' prefix. Lotus leaves do not have this problem because they continuously replace their waxy layer. Mixing titanium oxide into the film significantly alters how quickly stains build up. This is probably because titanium oxide reacts with dirt particles under ultraviolet light. The answer seems to lie in the titanium oxide concentration.