Actually the underbody is lead or aluminum sheet trimmed to shape. Many flyshops have a sticky back variety that works quite nicely. I too have problems with mylar tubing unraveling. I think that one needs to attain guru status to deal with this material. Maybe about the time you figure out spey winging techniques. I basically expect to lose some when I tye it on. I slide it down the hook past the frayed section tye it off in the good area, and trim the fraying down. If someone has a better way of doing it, please let us know. Rob --------- Genetic pollution damages wild stocks, bonk those Hatchery Zombies!