Abstract: A return air barrier for a system for venitilation of the passenger compartment of a motor vehicle has a closure flap made of a flexible low-density material suspended, and resting by its own weight against an inclined grid in the housing of the return air barrier, and during air flow moves against the direction of outflow into the closed position. Above the closure flap within its range of travel thereof, there are several hook-like webs mounted in such a way that at the height at which flapping begins, the flap touches the free end of at least one web and, with increasing air velocity, buckles in the lower edge region, adheres snugly to the webs and is held in an angular form.