A seatback assembly is provided having a thoracic support structure. The thoracic support structure includes a center portion extending in an upright direction and is adapted to be positioned adjacent the seatback to align adjacent a thoracic region a user's spine. The center portion is formed of a first foam material having a first hardness. A pair of side portions are disposed adjacent to and connected with the center portion. The side portions are formed of a second foam material having a second hardness. The first hardness is greater than the second hardness for providing support to the user's spine. An adjustment mechanism is connected to the thoracic support structure for positioning the support structure along the seatback so that the center portion provides support to at least a portion of the thoracic region of the user's spine.