Abstract: Lightweight chair from a single unitary die-cut and scored generally rectangular blank of sheet material which is collapsible for easy storing and carrying, and which pops open for easy set-up. The lower 10-20% of the blank has a plurality of flaps gulable to the inner face of adjoining sidewall panels to form a reinforced base perimeter. Half of the blank forms the chair base sidewalls, and the remaining upper half forms a pair of adjoining seat/back panels which are delineated from the sidewalls by a set of generally W-shaped score lines. An assembly tab at one end is fastened to the opposite side of the other end of the blank to form in cross-section an enclosed polygon, preferably a modified hexagon of unequal sides. A first of the pair of seat/back panel assemblies is folded down with one or more tabs or flaps frictionally engaging one or more of the sidewall panels.