I use either PIGMA (because they are truly permanent, and there are LOTS of colors) or SIGNO roller ball pens (I get them at Sam's Club, and they are permanent after heat set, also smoother to write with on fabric due to the roller ball). I think Sharpies bleed too much and the writing turns out fuzzy looking. I also iron fabric to a piece of freezer paper and run it through the printer then heat set, works great too.