An airbag unit with an airbag exhibiting an impact surface, a housing, a gas generator, a first tensioning element extending from housing to impact surface, which is interrupted when the airbag is fully expanded, and a second tensioning element extending from impact surface to an outlet valve with variable cross section located in airbag. The cross section of the outlet valve becomes smaller when the second tensioning element is under tension. In order to ensure a high degree of functional reliability, outlet valve exhibits a nozzle extending around an opening, around which the second tensioning element is guided.