I use either Permacore or Glide. I do have a spool of signature which is all cotton and my experience was that it breaks a lot. I tried to use it when I first got my Gammill and I did get frustrated with it rather quickly. Now that I am more experienced, I probably wouldn't have that much of a problem. Both Permacore & Glide are polyester so they are stronger and would probably work better for you at the beginning.