A B-pillar is shaped from a sheet blank (20,21) into a hat profile with a central flange (12), two sides (13,14) and two side flanges (15,16), and it has, over a portion of its length, a reinforcing sheet (21) that make the B-pillar have double sheets. The reinforcing sheet (21) extends out over the side flanges (15,16) over at least ¼ of its length and narrows down at both its ends so that it does not extend out over the side flanges over part of its length.