Economical stacked office chair. The seat and back are made of black polypropylene, which gives the chair its superior durability and lumbar support. The chair has a solid chrome frame and the sculpted seat back has an opening integrated into it for enhanced ease with mobility and stacking. These chairs can be stacked up to 16 high on a dolly (Boss D100, sold separately), or 5 high on the floor whichwill save storage space as well.Ganging clamps are also available (Boss B1400GC, sold separately) so that multiple units can be attached at the bottom of the leg.