Scientific Anglers XTS Gel Spun Polyethylene. If you're looking for the best backing available, nothing can beat the XTS gel spun backing. With a diameter a fraction of the standard material, XTS retains its strength in the water, offers extreme abrasion resistance, and can fend off the worst the elements have to offer. *Note: Because Scientific Anglers XTS Gel Spun backing is so thin and slick, knots should be carefully tied, tightened and tested before use.