The leader is concerned with the connection between fly line and fly and it can conveniently be thought of as three parts, the butt which attaches to the fly line, the taper which provides the transition between the butt and the tippet controls the energy flow and fine-tuning the characteristics of the leader and the tippet that provides the final connection to the fly. All parts of the leader are important but they need not be complicated and certainly should never contain any more pieces of monofilament than is necessary to achieve the desired result. Ultimately it is you who must be happy with the way that your leader performs but beware; leader design cannot compensate for faulty casting technique, but bad leader design may well cause poor presentation and exaggerate the effect of casting faults.
Fly line manufacturers take great pride and care in designing the profile and tapers of their products. The front taper of a fly line is designed with the purpose and range of likely fly sizes to be encountered in mind. For best results the join between fly line and leader should be as non obtrusive as possible and so a nail or needle knot connection is likely to perform better than a comparatively heavy and bulky braided loop attachment. Recognising the convenience and popularity of loops many of the latest designed fly lines come with small factory made neat and relatively inconspicuous loops for leader attachment which is a useful improvement for those who like to use loop connections and largely overcomes the criticism of braided loops.
Comparison of leader butt qualities
The leader butt section is attached to the fly line and should have characteristics similar to the tapered end of the fly line in order to transfer energy from the line to the butt section and hence smoothly along the leader. If the butt is too flexible it will hinge, if it too stiff it will be very difficult to control or make tight loops, the perfect transition will have similar flexure to the line itself. Three scenarios are illustrated and the suitability of the leader butt material can be judged by comparing the relative stiffness of the fly line and leader, if the leader is too flexible it will hinge at the join, if it is just right the transition will be smooth and if the leader is to stiff the fly line will be flexed by it.
The tapered section in the middle of the leader then transmits energy from the butt section to the tippet. Fly size, the target fish species and the prevailing conditions determine the preferred characteristics for the choice of leader make up materials. Proprietary knotless tapered fly leaders of many types and sizes can be purchased and these are suitable for lots of uses but for some situations it is better to custom make tapered leaders with materials of your own choosing or at least it is fun to experiment with different recipes for bespoke leaders to suit you purpose.
General purpose "standard" knotted tapered leader design
As a rule of thumb the common formula for general purpose leader design is approximately 60% butt, 20% taper and 20% tippet. These percentages can of course be adjusted according to purpose e.g. leaders for gentle presentation or to combat drag may have shorter butts and longer tapers and tippets and indeed the leader in total may be longer than normal whereas leaders for delivering a heavy or bulky fly will have extended butts, steep tapers and shorter tippets and the overall leader length is made shorter than normal. Nine feet is the most popular general purpose leader length and most are between that and 12 feet long. Much shorter leaders from 3ft upwards are commonly used for pike fishing and in conjunction with sink tips and sinking lines for salmon and steelhead where the short length helps to keep the fly down at the same depth as the line. Stillwater anglers occasionally use extra long specialised leaders up to 20 feet in length to achieve the most subtle presentation for buzzers but they can only be used in favourable weather conditions and casting direction.