To make the cushion for the bed, I started with three inch Project Foam, and wrapped it with two layers of batting.
Measure the fabric so that it is three inches wider on each side than the foam. My fabric was cut to 54 inches by 42 inches.
Fold the fabric in half with the wrong side out. Sew the two sides together. Flip the fabric so that it is right side out. One long end will still be open.
Slide the batting covered foam into the cushion cover. Fill the top of the cushion with a small amount of Poly-Fil cushion foam.
Pin the open side together, tucking the ends inside. Hand sew the edge closed.