Haven't tried Frixxion pens, but I did do a test with Crayola washable markers. I took a piece of the fabric I used for the sashing on my Plaid Obsession Quilt and made marks with each color. Washed it and was surprised to find that the blue washed out the best, followed by black. Orange and pink were the worst. So, this leads me to believe that certain colors of Frixxion would be easier to remove than others. I will never use something to mark a quilt without testing it first. I have learned from the heartbreaking stories told here.