Seat is fabric upholstered over foam that is applied to a molded polypropylene liner. Back is a frame of molded glass-reinforced nylon with 100% polyester mesh fabric. Torsion mechanism consists of two flat torsion springs captured at both ends by steel bushings welded to the backrest supports. Frames for four-leg chair are 15-gauge seam-welded tubular steel. Frames for sled base chair are 16-gauge seam-welded tubular steel.