I bought all the roller ball and highlighter colors of the Frixion pens.
They DO all return if they're exposed to freezing temperatures (as in the cargo hold of a plane when you ship the quilt) but the inks all wash out with just a light hand washing.
I think that a thorough washing in the washing machine would do even better.
You'd think that the ironing would permanently set the ink, but after washing and air-drying there was no trace of the markings and even freezing did not cause any trace of the ink to re-appear.
Test everything yourself of course. For myself, I've decided that they're just about perfect for marking fabric cuts, applique' placement, measurements for borders and quilting guidelines. I love them and I'm done using pencil, chalk and ceramic markers to the greatest extent possible.