The two major types of air spring are the rolling lobe (sometimes called reversible sleeve) and the convoluted bellow. The rolling lobe air spring uses a single rubber bladder, which folds inward and rolls outward, depending on how far and in which direction it is moved. The rolling lobe air spring is available with very high usable stroke length—but it is limited in strength because of its tendency to bulge, and therefore, has limited force capacity. The convoluted bellow type air spring uses one to three shorter bellows, with the multiple units being reinforced by a girdle hoop. Convoluted air springs are capable of ten times the force of a rolling lobe version and twice the life cycle rating, but have less usable stroke to work with.