Side airbag with necking chamber

A side airbag 18 for a vehicle (12 fig.1) comprising a main chamber 36 and a second, necking chamber 40. The main chamber has an opening 43 for connecting to an inflator 20 and a first thickness (T1 fig.5A) in an inflated condition. The necking chamber is peripherally surrounded by the main chamber and is connected to the main chamber by at least one restrictive vent 46. The necking chamber has a second thickness (T2) in the inflated condition less than the first thickness and is aligned with a targeted body area. The body area may be a pelvic region or rib-cage of a vehicle occupant (38 fig.3). A wall (44, fig.5B) may separate the main chamber from the necking chamber such that the vent may be disposed in the wall. The opening for the inflator may be located at a rear of the airbag in the inflated condition such that no vent(s) is on a rear side of the second chamber. Also claimed is a side airbag module (14 fig.1) comprising a housing (16 fig.2) which may be located in a seat back (28 fig.1) or B-pillar (26) of the vehicle.