Side airbag apparatus

A side airbag apparatus (13) for vehicle has an airbag (16) and an inflator (15). An upper chamber (18), a lower chamber (19), and an intermediate chamber (20) are defined by a seam (17) in the airbag. When the airbag is deployed, the upper chamber corresponds to a shoulder of an occupant, the lower chamber corresponds to a lumbar region of the occupant, and the intermediate chamber corresponds to a thorax of the occupant. The seam guides gas from the inflator to the upper and lower chambers such that the upper and lower chambers are substantially simultaneously inflated, and the intermediate chamber is inflated after a delay. The thickness of the intermediate chamber is less than the thicknesses of the upper and lower chambers. As a result, the occupant of the vehicle is effectively protected.