Cigarette filters are made of cellulose acetate, a type of plastic fiber. The cellulose acetate fibers are thinner than sewing thread, white, and packed tightly together to create a filter that can look like cotton. Other materials have been tried and rejected in favor of the taste that acetate produces. The filters are specifically designed to absorb vapors and to accumulate particulate smoke components, prevent tobacco from entering a smokers mouth, and provide a mouthpiece that will not collapse as the cigarette is smoked. Filters vary in filtration efficiency, depending on whether the cigarette is to be "light" or regular.