Material: HDPE (High Density Polyethylene)Blow molded seat, Double-wallAverage Thickness of single layer: 3.5mm Steel stands, integrated with armrestUltraviolet light protection treatment for indoor/outdoor useUpholstered seat and back with 3mm PU foam and covered with fabricThese tilt-up seats can be fitted directly on vertical surface of the concreteCenter distance between chairs: >=495mm; 500mm recommended.