A seat assembly includes a seat fabric, wherein at least a portion of the seat fabric comprises a yarn comprising a shape memory polymer adapted to undergo a change in a modulus of elasticity at a thermal transition temperature; a support material upon which the seat fabric is disposed; and a controller in operative communication with the shape memory polymer, wherein the controller is operable to selectively apply a thermal activation signal to the shape memory polymer to effect a change in the modulus of elasticity of the shape memory polymer, wherein the change in the modulus of elasticity of the shape memory polymer results in a change in a stiffness and/or flexibility of the seat fabric.