A chair back assembly includes a substantially rigid peripheral frame defining a central opening, and a substantially flexible back shell coupled to the peripheral frame and spanning at least a portion of the central opening, wherein a first portion of the back shell is fixed with respect to the frame at a first position, a second portion of the back shell is fixed with respect to the frame at a second position that is different than the first position, a third portion of the back shell is constrained with respect to the frame in at least one direction of motion at a third position located between the first position and the second position, and wherein a fourth portion of the back shell is free from constraint with respect to the frame at a fourth position located between the third position and the second position.