A seat includes a seat back having a frame and a cover, an impact absorbing device, and an actuator in communication with the impact absorbing device. The impact absorbing device is movable from a stowed position to a deployed position. The impact absorbing device includes a base connected to the frame, a panel adjacent to the cover in the stowed position and spaced from the cover in the deployed position, and an intermediate portion connected to the base and the panel. The intermediate portion defines a chamber between the base and the panel. The intermediate portion has a portion thickness and the panel has a panel thickness greater than the portion thickness.