Open Loop: Best for nymphing when using split shot and or a 2 fly rig and casting heavy flies. The wide loop as pictured insures a two fly rig does not get caught up in itself. It dissipates enough energy so a weighted fly doesn't "kick" when it reaches its end. It also decreases the chances of a tailing loop thus decreasing tangles.

Closed Loop: Best for casting into the wind and for increased distance. Tight loops can be obtained by using a short casting stroke with the tip of the rod stopping at the 11:00 to 1:00 range. Open this arc and the loop will increase in size.