Never use nylon anymore! It was never satisfactory to start with because it stretched, messed up the machines and cut the fabric. I like to use Bottom Line thread from Superior to do the things I used to do with polyester monofilament thread. It is a fine polyester thread. I use it on top to stitch in the ditch to anchor my blocks before I do the decorative quilting. It disappears completely after I wash the quilt. I have mixed feelings about using it in the bobbin. It works quite well but I like my quilting to show on the back of the quilt.