TushGuard Seat Cushions - Memory Foam Cushion for Office Chair, Car Seat, Airplane, Bleacher - Sciatica & Hip & Coccyx Pain Relief Desk Chair Cushion for Long Sitting Office Workers, Car Drivers. Large size measures 18" wide x 14" deep x 3" thick (at thickest spots) $15 for a used one - like new, and $20 for a new one - never opened.