Place two 18-inch by 18-inch sections of vinyl fabric together with the outsides facing inward to each other. Line up all four edges of the fabric.
Stick straight pins around the perimeter of the vinyl fabrics, leaving a 1/2 inch border around the edges.
Thread a sewing machine with heavy duty thread and place the two sections of vinyl, pinned together, into the sewing machine.
Sew around the edge of the vinyl fabric, beginning at a point three inches from one corner. Sew around the entire perimeter of the vinyl fabric until you reach a location 6 inches from the starting point. You will need to leave one corner unsewn to allow you to stuff the cushion.
Remove all straight pins from the vinyl fabric and pull the two sections slightly apart at the opening. Reach inside and pull the exterior side of the vinyl outward to display the pattern or color. Poke the corners from inside to open up the vinyl entirely.
Stuff the cushion with pillow stuffing. Insert as much stuffing as you can without having any protruding from the open corner. Stick straight pins in the opening to seal it shut.
Sew the opening by hand with a heavy duty sewing needle and thread. You should sew around the opening two or three times to create a strong hold.