Hi Pedro -
I did some checking around today for the upholstery cord. I checked with a local shop and found there to be several different cord options. The cording he stocked was about 3/8" dia. and had a tissue core with some kind of nylon webbing around it. He looked in his supply catalog and found the cord to also be available in cotton.
I then went to a local fabric store (Hancock Fabrics) and found that they stock the cotton cording made by Conso Products Co. (http://www.conso.com). I noticed that you didn't mention in any detail, the size and material type of cording you used in your last report. Can you please shed some light on this?