There has been some negative reporting on the Fix-On pens. While the lines do disappear and return if cold, the cold reference is usually mentioned when putting the quilt in the freezer. Who puts their quilt in the freezer...However, they might (do) return when left in a cold room over winter. Also the one report from a highly respected quilter said that even with washing, the lines will return but very dim. The quilter posted on one of the other sites but believe she might also have a web page. Her test was very thorough.