A cushion for a wheelchair, including a matrix of cushion modules, wherein each cushion module includes a cushion element that has a phase change material included in its filler material that sits above an additional cushion element of a larger volume of filler material. The cushion also typically includes a support rail located on three sides of the matrix of cushion modules to align the body of the wheelchair user when sitting in the wheelchair. In addition, the cushion typically includes a base member that is positioned beneath the matrix and provides stability for the cushion. The cushion elements are typically enclosed in a moisture resistant envelope.