A landfill is a carefully designed structure built into or on top of the ground in which trash is isolated from the surrounding environment (groundwater, air, rain). Although findings differ slightly, in 2006 approximately 26 percent of materials entering landfills were paper products, 18 percent food scraps, 16 percent plastic, 9 percent rubber, leather, and other textiles, 7 percent each of yard waste, metals, and wood, and 6 percent glass. This does not, however, reflect actual landfill content at any point in time since some materials decompose faster, or compact better, than others.