Applying the same cord to two pillows turns them into a set.
Cut 3/8-inch-thick cording 2 inches longer than the pillow's perimeter.
Use a seam ripper to make a 3/4-inch opening in the pillow's seam.
Tack both sides of the opening to prevent further ripping.
Tuck 1 inch of the cording into the gap; sew it to the seam with a slip stitch (we used red thread for visibility, but you should choose a matching color).
Sew around the pillow, then insert the cord end into the opening, and stitch closed.