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Rainproof fabric. Coloured scanning electron micrograph of the surface of a waterproof fabric used in outdoor clothing. The coating is polyurethane, and has many tiny pores. These allow humid air and water vapour to come out of the garment, but the small size prevents liquid water from entering due to surface tension. This type of coating is known as 'breathable waterproofing'. Magnification: x30 at 6x7cm size. x105 at 10x8ins (KEYSTONE/SCIENCE PHOTO LIBRARY/SCIENCE PHOTO LIBRARY)