In a method of folding an airbag (10) for a vehicle occupant restraint system, especially of curtain-type side airbag, to form an airbag package (12′), the airbag (10) is rolled and/or folded to form an airbag roll (12) having a first volume (V1). The airbag roll (12) is fed to a pressing device (14) in which the airbag roll (12) is compressed to form an airbag package (12′) having a second volume (V2) which is smaller than the first volume (V1). The airbag roll (12) and, resp., the airbag package (12′) is heated within the pressing device (14) and the airbag package (12′) is cooled, with the airbag package (12′) retaining the second volume (V2) when it is removed from the pressing device (14; 114). The pressing device (14) includes a pressing mold or a molding shaft (18) whose height substantially corresponds to the desired height of the finished airbag packages (12′), a heating unit (20) for heating the airbag packages (12′) and a cooling device (22) for cooling the airbag packages (12′).