Your best bet is to buy one and test it yourself, that is what I did. I posted under Quilt in the freezer. I love them for drawing Red Work embroidery patterns because I stitch over the line and then erase any bits showing with the iron. I also like them for small sewing items. They definitely have a place in my sewing room. Would I use then to mark quilting lines on a quilt going to a show? Probably not but I have seen on major quilt blogs where others do. Frixion pens are like asking if you pre-wash fabric or not, it is a personal choice.