From Blue Sky Furled leaders

"How is a furled leader different from a braided leader?

Our furled tapered leader is not a "braided" leader. Conventional braided leaders have a hollow center that tends to pick up and hold water which in turn makes the leader heavier and effects casting performance. When cast, a braided leader also has a tendency to 'splat' the surface of the water and spray the small droplets contained in its core. Many say that these negative characteristics put down or "spook" fish. BlueSky furled leaders have a sold core and do not have these negative characteristics. Additionally, most braided leaders are too limp to fully turn over the tippet and fly."