I used Royal & Langnickel Nano-Liner Drawing Pens in black and blue, size 5. I bought a 4 pack on Amazon that had 4 colors for about $11. I tested them on laundered fabric (no fabric softener) and the red and green ones faded and washed out. The blue one and black ones did equally well whether I heat set them or not. I will definitely use them for future projects. Thanks for all your positive comments!