I'm another Frixion lover. I use them almost every day. Today, I was using them to mark where to position my ruler for cutting. Since I was cutting on the marked line, it didn't matter about bleaching.
I love the fact that the markings come back with cold. I am making a Redwork BOM that has a rather complicated design that has to be traced on to the fabric. I use the black Frixion pen to trace the design. Then I iron a sheer interfacing to the fabric so that my knots will not show through. Now my design is gone! A quick trip to the freezer and the design is back, ready for embroidery. I love those Frixion pens!