Ergonomic Backrest Stacking Chairs (Set of 4)Ergonomic Backrest: Curved design conforms to the human back for enhanced comfort and posture support Durable Construction: Injection molded polypropylene seat and fiberglass reinforced back shell for lasting performance Stable Tripod Base: High strength 11mm solid steel with arch shaped structure ensures robust stability Heavy Duty Load Capacity: Tested to support up to 180KG with rigorous tensile and cycle testing Easy to Move: Hollow seat design