Whole tobacco can also be processed into a product called expanded tobacco. The tobacco is "puffed", or expanded, by saturating it with supercritical carbon dioxide and heating the CO2 saturated tobacco to quickly evaporate the CO2. This quick change of physical state by the CO2 causes the tobacco to expand in a similar fashion as polystyrene foam. This is used to produce light buy cigarettes by reducing the density of the tobacco and thus maintain the size of a cigarette while reducing the amount of tobacco used in each cigarette.