although composed mainly of shredded tobacco leaf, use a significant quantity of tobacco processing byproducts in the blend. Each cigarette's tobacco blend is made mainly from the leaves of flue-cured brightleaf, burley tobacco, and oriental tobacco. These leaves are selected, processed, and aged prior to blending and filling. The processing of brightleaf and burley tobaccos for tobacco leaf "strips" produces several byproducts such as leaf stems, tobacco dust, and tobacco leaf pieces ("small laminate"). To improve the economics of producing cigarettes, these byproducts are processed separately into forms where they can then be added back into the cigarette blend without an apparent or marked change in the cigarette's quality. The most common tobacco byproducts include: Blended leaf (BL) sheet: a thin, dry sheet cast from a paste made with tobacco dust collected from tobacco stemming, finely milled burley-leaf stem, and pectin. Reconstituted leaf (RL) sheet: a paper-like material made from recycled tobacco fines, tobacco stems and "class tobacco", which consists of tobacco particles less than 30 mesh in size (about 0.6 mm) that are collected at any stage of tobacco processing: RL is made by extracting the soluble chemicals in the tobacco byproducts, processing the leftover tobacco fibers from the extraction into a paper, and then reapplying the extracted materials in concentrated form onto the paper in a fashion similar to what is done in paper sizing. At this stage, ammonium additives are applied to make reconstituted tobacco an effective nicotine delivery system. Expanded (ES) or improved stem (IS): ES is rolled, flattened, and shredded leaf stems that are expanded by being soaked in water and rapidly heated. Improved stem follows the same process, but is simply steamed after shredding. Both products are then dried. These products look similar in appearance, but are different in taste. According to data from the World Health Organization, the amount of tobacco per 1000 cigarettes fell from in 1960 to in 1999, largely as a result of reconstituting tobacco, fluffing, and additives. A recipe-specified combination of brightleaf, burley-leaf, and oriental-leaf tobacco is mixed with various additives to improve its flavors. Most commercially available cigarettes today contain tobacco that is treated with sugar to counter the harshness of the smoke. Additives Various additives are combined into the shredded tobacco product mixtures, with humectants such as propylene glycol or glycerol, as well as flavoring products and enhancers such as cocoa solids, licorice, tobacco extracts, and various