Frixion Rollerball pens

Heard about these pens from a friend. The ink of these pens erases due to the heat created by friction. So this means they're great for marking fabric when you don't want the marks to be permanent. The idea is you mark your fabric, sew over and iron to remove the ink. I have only really used them on cotton fabric and love them. The only down side is if you mark a white/cream fabric and remove with the iron without stitching/quilting/painting on top, there is a very faint yellow trace left behind so would not recommend for use on topside if not sewing over. Wish they did a pen for darker fabrics.