This tube material is not quite rigid. Its a little soft so that when you are tying the fly with the tube on the mandril you can use say six wraps of flat waxed nylon to compress the tube near the end then dress the fly over the top of this constriction. What this accomplishes is a slight constriction through which the hook eye will not pass. This eliminates the need for a short section of soft tubing to hold the hook. Just one less thing you have to mess with.