I have purchased 2 packs of the pens (red, blue, black) but have not used them yet or even tested them on any scraps. I tend to agree with catrancher regarding the temperature issue. I don't think I'll be putting my quilts into the freezer nor will I keep my thermostat below 38 degrees (I hate being cold). I seem to remember reading somewhere about heat setting them with your iron prior to washing/drying. I'll definitely test them for myself before using on a project.