There have been many discussions of the Frixion pens on here. I have purchased them at Walgreens and other stores. I ran my own test with them. I picked 10 different fabrics from my stash. Cut off a little piece and scribbled on them with a Frixion pen on both ends. One end I ironed the ink off the other I left it on and washed them in warm water. Most of the un-ironed ink came out in the washer and all of it disappeared in the dryer. I them threw the samples in the freezer. The results varied by fabric. Some had faint lines and some had no lines. A FMQ teacher at a LQS says that washing in Orvis soap removes all of the residue from the pens. I haven't tested this yet. I use them all the time and absolutely love them.