From Sublime Stitching:
Finally! An iron on, heat transfer pen with a fine tip! Exclusively from Sublime Stitching. I developed these pens for embroidery artists like you, looking for creative solutions. These pens create delicate, visible, pattern lines that are easily covered by the tiniest stitches. Use these with PDF printout patterns, iron-on transfers that no longer imprint, or your own original designs! The ink will transfer to pre-heated fabric (and also wood and cardstock) with a hot, dry iron.
Black pens are sold separately.
Please note: The YELLOW pen works best as a color fill marker, is visible only on white fabric, and does not work well for making visible contour (line) drawings.
Ink is permanent. Be sure to preview these results of each color after transfer. They do not appear on black fabric (go here instead for help with that)!
Any fresh copy paper will work with these pens. But if you need tracing paper, I recommended my Heavy Duty Tracing Paper for consistent results.