Follow along with librarian Jennifer as she demonstrates capillary action with this easy and colorful experiment. Capillary action is the spontaneous flow of a liquid into a narrow tube or porous material, like paper towel. See how two different types of markers react very differently with water: washable markers, which flow smoothly; and permanent markers, which form a thin, elastic layer. All you need is a paper towel, a permanent marker, a few washable markers, a bowl, and water.