Hermell Products WC4440BK Wheelchair Cushion, 16 by 18 by 4-Inch, Black by Hermell Products Inc.. $22.23. Wheelchair cushion with black polycotton zippered cover. Even support. Durable and comfortable. Wheelchair cushion foam just the correct length and width, but available in three thicknesses. The cushions are constructed of durable polyurethane foam for even support, durability, comfort and long life.