Take the curtain off of the curtain rod, then lay the curtain flat. Measure the width of the curtain using a measuring tape.
Cut a piece of 2-inch-wide ribbon to measure the exact width of the curtain.
Cut a piece of decorative cording to measure the width of the curtain plus 4 inches.
Lay the cording across the width of the curtain, positioning the cording evenly in the middle of the curtain's length.
Lay the ribbon widthwise over the cording, positioning the cording in the center of the ribbon.
Pin the long edges of the ribbon along the entire length of the ribbon using straight pins.
Sew along the pinned edges using a sewing machine, then remove the straight pins.
Tie a knot into both ends of the cording, which prevents the decorative cord from slipping back through the ribbon casing.
Hang the curtain back onto the curtain rod, then cinch the drawstring to open the curtain.