Abstract: An inflatable restraint system having a head/thorax air bag cushion configured to protect the head and thorax regions of a motor vehicle occupant during a side impact collision. The air bag is configured to be kidney shaped when inflated to optimize the protection area while eliminating excess volume. The air bag is inflated from the bottom up, thus inflating the region adjacent the thorax area of the occupant first. As the thorax area is loaded by the occupant, gas is forced into the head area of the air bag. As the head area is loaded by the occupant, gas is vented to atmosphere through vents located in the head area of the air bag.