Cushion is uniquely designed with a gel filled chamber which is encased in soft foam and covered with a 20 gauge heavy duty vinyl pouch. Gel foam combination helps prevent cushion from flattening, promotes seating stability for maximum comfort and conforms to body contours. Convenient rear tie straps hold cushion securely in place. Removable, machine washable, three way stretch fabric cover with waterproof backing. Foam meets CAL #117 requirements