A knee airbag module of a vehicle occupant restraint system comprises an outer housing (14) in which an airbag (20) folded into an airbag package prior to its deployment as well as an inflator (16) generating filling gas for filling the airbag (20) are accommodated. In the outer housing (14) an exit opening (22) is formed through which the airbag (20) leaves the outer housing (14) during deployment. The airbag (20) is subdivided into plural chambers (28a-28f) arranged in series and being in fluid communication. The chamber closest to the inflator (28a) is separated from an adjacent chamber (28b) by a wall (32) which in the inflated airbag (20) extends substantially in the area of the exit opening (22) along the exit opening (22).