The invention relates to a side airbag device (1) for vehicles, comprising at least a first and a second material layer (10.1, 10.2) for forming an airbag (10) having at least one chamber (12) that can be inflated by means of gas. In the inflated state of the airbag (10), the first material layer (11.1) extends in a vehicle longitudinal direction (x direction) and the second material layer (11.2) lies opposite the first material layer (11.1). The first and second material layers (11.1, 11.2) are connected to each other along at least a first edge section (11.11, 11.21). According to the invention, in the inflated state of the airbag (10), the first and second material layers (11.1, 11.2) each have a first edge section (11.11, 11.21) extending in a vehicle vertical direction (z direction) and a second edge section (11.12, 11.22) extending in the plane spanned by the vehicle longitudinal direction (x direction) and the vehicle transverse direction (y direction), the first edge sections (11.11, 11.21) of the first and second material layers (11.1, 11.2) are connected by means of a first seam (13) that at least partially bounds the chamber (12), and a second seam (14) is provided, which is formed by the second edge sections (11.12, 11.22) and bounds the chamber (12) additionally to the first seam (13) and extends transversely to the first seam (13).