Often you don't have a cord on hand or want to choose a really matching color - then you can simply adopt the trick from Franziska Bünzen of the label Küstenkind.
She uses our wool braid for this. The photo here on the blog shows the braid sewn on.
Quick guide:
+ Finish the short side by folding it over and sewing it closed
+ then sew along the long edge
+ shortly before the end, fold the second short side inwards by about one centimeter, then fold the long edge over it and finish sewing the rest of the long edge.
Finished. Beautiful. Can be used for anything that requires cords.