1. With wrong sides inside, fold two solid cream 16-1/2x20-1/2" rectangles in half to form two double-thick 10-1/4x16-1/2" rectangles. (The double thickness makes the pillow back more stable.) Overlap folded edges by about 4" to make a 16-1/2" square (Pillow Back Assembly Diagram). Baste around square to make pillow back.
2. With right sides together, layer quilted pillow top with pillow back; pin. Sew together around outer edges. Turn right side out. Insert pillow form through opening to complete pillow.