Reflex Stack Chairs feature a unique spring back lumbar support that promotes correct posture throughout the day. The self-adjustable lumbar panel (9-1/4" wide) is activated by a unique spring mechanism once weight is applied for comfort and back support tailored to the individual user. Seat and seat back are made of durable contoured plastic, and the frame is made of chromed steel for superior strength. Seat measures 17" high x 17-1/2" x 18" deep while the back measures 15" high x 19-1/2" wide. The sled base includes transparent plastic feet to protect the floor surface and to prevent slipping. Chairs stack 12 high.