I used to make my own clothing labels from printable inkjet iron-on transfers, back when I was doing more bridesmaids dresses than wedding alterations. Definitely use 100% natural fiber, the more tightly woven the better, there's less chance of weave 'shiftage'. A thick cotton or a heavy wool should take the ink better. Be absolutely sure not to 'wiggle' the iron, don't slide it, lift and press. It may vary depending on what brand of printable transfer you use but I found it worked better without steam. Be SURE to do a test patch.