Side airbag for installation in a motor vehicle, the vehicle seat with such side airbag and vehicle

It is described with such a vehicle seat side air bag for installation in a motor vehicle, a vehicle seat with such side airbag and a motor vehicle. The side gas bag has at least one fastening device for fastening of the side airbag to the backrest (24b) of the vehicle seat, an outer shell (12) having a viewed in the direction of the vehicle forwardly extending first side wall (14a) and means connected to the first side wall second side wall (14b ) on. In order to protect the occupant to be protected with minimal effort better from moving toward the vehicle center, the second side wall (14b) extends at completely filled, external forces free of outer envelope substantially transverse to the vehicle direction, such that at least (a third side wall 14c) is provided, which connects the first two side walls with each other