through a slit on the base of the housing 40 as the traction bands 30 to 36 are guided through the slits 42 and run on alternate sides of the gas bag through the exerting of traction on the traction bands a controlled folding of the gas bag is brought about the spacing between two adjacent slits 42 is designated by b in fig4 it determines the width b of the folded gas bag 10 inside the housing 40 as can be shown by simple geometric considerations in the spacing a from the lower edge 10a of the gas bag 10 each traction band 30 to 36 is provided with a hole 46 at this hole 46 the respective traction band is hooked on a bent out lug 48 on the outer side of the housing 40 the traction bands 30 to 36 thus remain under tension in order to ensure the folded state of the gas bag inside the housing 40 during mounting in the vehicle on completion of mounting the open end of the housing 40 which is u shaped in cross section is closed by a covering which also holds the gas bag inside the housing the traction bands 30 to 36 can now be released from the projecting lugs 48 on the base of the housing 40 so that on activation of the gas bag they do not impede its unfolding alternatively each traction band 30 to 36 is provided.