Poli-flex nylon (from SignSeen) is a specially made tape for hydrophobic and nylon surfaces, such as sports-clothing.
A few notes on using this stuff:
-It's thicker than usual flex-flock films, so you need to set the blade a fraction deeper. Use the test function for this. I did not do this, and ended up with a lot of almost cut corners, making the weeding very tiresome.
-The blade should make a noise as if it's scratching the polyester liner. It shoud not cut through the liner, that will wear the blade down very quickly.
-Your artwork should be cut in mirror image, since you are cutting from the backside of the image.
-The sticky part is already the adhesive, so prevent touching it or making it dirty.
Using a handhold iron:
-It works (somewhat) but the temperature distribution is very uneven. Slightly below the cotton setting the temperature should be 155 degrees Celcius. On my iron there are spots that were hotter (160) as well as cooler (145). When I started moving the iron around, the artwork distorted a minor amount and I saw glue being forced from under the letters.