A side airbag (10) for a motor vehicle comprises an airbag shell that surrounds a gas compartment and has at least one opening. A hose (20) has an outlet opening (22) and is located on the outside of the airbag shell. When the hose is in a state in which it is not under pressure, the hose connects the opening (16) to the outlet opening (22), and thereby to the surrounding area. The hose (20) comprises a first section (20a), which is situated at the height of the opening (16), and a second section (20b), which connects the first section (20a) to the outlet opening (22). The ventilation arrangement composed of the opening (16) and the hose (20) is used to make the side airbag hard for a large occupant and soft for a small occupant. In order to improve the behavior of the side airbag for a small occupant, without impairing the behavior thereof for a large occupant, the maximum cross-section of the first section (20a) is larger than the minimum cross-section of the second section (20b).