Thunder (Granite) Hammock Seat Cover Luxurious microvelvet fabrics with rugged nylon backing. Tufted, polyester-filled bottom cushion provides added comfort. Front and back flaps with adjustable nylon straps and clips attach securely to front and back seat headrests. Rigid foam-filled sides contain dirt and pet hair and can be unclipped to allow easy entry for your pet. Slits in bottom seat cushion allow use with seat belt.