Seat frame, in particular backrest frame and/or seat frame for a vehicle seat

The structure (1) e.g. backrest frame (2), has a plug-in type, flexible support unit (11) arranged at an edge facing a passenger, where the edge is chamfered with radius and is formed in arch-shape. The radius of the edge amounts to 0.2 to 0.05 of height of a side beam (3). The edge exhibits behavior corresponding with a curved path following a contour of the passenger, and runs at an angle of 30 degree to 80 degree to a base of the side beam. The support unit is pivotably arranged at an axle and is formed from plastic material.