Among other things, a piece of furniture is formed from three separate precut pieces of flat cardboard. A first one of the pieces has a bottom edge to rest on a floor with the first piece rising vertically from the bottom edge and has at least one slot at an upper edge of the first piece. A second one of the pieces has a bottom edge to rest on the floor with the second piece rising from the bottom edge and having at least one slot at an upper edge of the second piece. A third one of the pieces has a crease across the piece and at least two slots along at least one edge that is parallel to the fold. The piece of furniture is formed by mating the one slot in the first piece with one of the slots of the third piece, folding the third piece of cardboard at the crease, and mating the one slot in the second piece with another one of the slots of the third piece, with the third piece folded along the crease.