Another innovation of this PK91 folding stool was the way it folded flat. In a typical stool, the identical frames are nested one inside the other, which causes them to be offset when the stool was folded. Kjaerholm wanted his stool to appear consistent from both sides, folded or unfolded. The PK91 achieves this because of two design features: First, the points of contact between two frames consists of ball bearings flush joints. Second, the frames are mirrored parallelograms with corners of 88 and 92 degrees. The proportion of the seat conceals this distortion and creates the appearance of the identical, nested frames.