A chair back assembly includes a substantially rigid back frame assembly, a back shell member operably supported by the back frame assembly and including a laterally extending top portion, a laterally extending bottom portion and a pair of longitudinally extending side portion extending between the top portion and the bottom portion and cooperating therewith to define an open space therebetween, wherein the pair of side portions are substantially rigid in a lateral direction, and wherein the back shell member is substantially rigid in a lateral direction and substantially flexibly resilient in a fore-to-aft direction, and a cover having a first surface adapted to support a seated user and a second surface opposite the first surface, wherein the cover is positioned over the back shell member to cover at least a portion of the open space.