Frixion Heat Erasable Pens from Pilot

Note: ALWAYS test your pen/pencil/whatever with your fabric and ensure erasability before using it for your embroidery project. Heat makes the ink visibly disappear, but the ink is still on the fabric and may someday reappear!

Frixion erasable pens from Pilot erase with friction (the eraser on the end) and heat. These sneaky pens do work on fabric and can be erased with an iron or hair dryer. 

BUT, they are a bit controversial. The ink can reappear when exposed to very cold temperatures. However, the lines can be erased again with heat. The long term effects are not known so please know the risk before using them on an embroidery project.

I like to use these pens on Kona cotton. I use them to note color gradients and stitch direction on the fabric, and they are later covered by my stitching.