I hand did this for my cat quilt, I have hidden figures like my initials and other things. I ended up using cording meant for blinds as a cost effective way to do this. I wanted white and washable, the thickness was right for me and it was cheaper than bought cording, plus I was concerned about shrinkage potential.
It's part of the "let's take a simple project and make it more difficult" way I think...
Edit: The top cord I was fighting with and trying to straighten out instead of letting it do it's own thing... you can see it's being difficult while the side one is nice and smooth.