the present invention relates to improved single - use bioreactors comprising disposable plastic bags for cell cultivation . the invention provides an inflatable bioreactor bag for cell cultivation comprised of a top and a bottom sheet of polymer material that are joined along their edges to form a sealed bag , wherein two opposing edges are formed as clamping edges to allow clamping of the bioreactor bag to a rocker type bioreactor , and wherein the bioreactor bag is provided with a wrinkle preventing structure at each end of the clamping edges . the bag avoids formation of undesired wrinkles or creases which otherwise lead to fatigue of the plastic and eventually fracture .