Water repellent surface. Close up of a water droplet resting on a water-repellent coated surface. The coating contains inorganic nanoparticles that increase the contact angle between the surface and water. The larger the contact angle, the more hydrophobic (water repellent) the surface becomes, until the water droplet forms a near-spherical shape which collects dirt as it rolls off the surface. This self-cleaning and waterproof property is known as the 'lotus effect,' and is named after the same properties found on the lotus leaf. Materials covered with this coating are able to withstand corrosion and maintain a clean surface. Photographed by Seashell Technology for the US Airforce, USA.