Lightweight seat for high-density configurations and cluster of adjacent seat, the seat comprising a support structure (10) supporting a seat pan (20) comprising a rigid shell (21), a lining (23) and an intermediate foam (22), and a backrest (30), wherein most of the rear portion (20A) of the seat pan (20), covering at least one rear third thereof, and at least left and right rear corner regions (20L, 20R) contained within a 10 cm radius from the left and right rear corners, have a thickness equal to or less than 25 mm or 15 mm, and in a front portion (20B) of the seat pan, covering at least a front third thereof, the rigid shell (21) defines a descending slope of at least 15 towards a front edge of the seat pan (20) and the intermediate foam (22) defines a wedge of at least 15.

A portable rocking chair includes upper and lower support seats, being mutually limited and movably connected. The upper support seat is connected to one or more rear support rods, and the lower support seat is connected to one or more rear support legs. Upper ends of one or more front support rods and the rear support rods are jointly connected to a chair fabric, which has a seat area and a backrest area for supporting buttocks and back of a human body respectively. When the rocking chair is unfolded, one or more front support legs, the rear support legs, and the front support rods remain at a stationary position relative to the ground. The rear support rods swing back and forth following movement of the upper support seat relative to the lower support seat, thereby driving the backrest area of the chair fabric to tilt forward or rock backward.