Read the product literature on leader and tippet materials and you see descriptive phrases like these: "more flexible," "slightly softer," "greater suppleness," and "pliability." It is clear that we should buy these products because they promise us a tippet that allows the fly to follow every current nuance without drag. The claims seem reasonable as well as persuasive. But how do we know which claim to believe? What is the standard of comparison if we simply get claims of more or better?

This chart shows the inherent stiffness 12 major brands when comparing materials of equal diameter.

Confused? This article, I believe, will clear up some of that confusion.

In an separate article, I discussed the strength and stiffness of different leader materials. [See "Fluorocarbon Tippet Versus Monofilament," July 2003 Fly Fisherman. The Editor.]

Measurement of leader stiffness was not part of my original plan. But since I was testing tippet materials in the lab anyway, I was asked by several curious fly fishermen to measure the stiffness of the same materials.

Each person I talked to, prior to beginning our work, had strong opinions. All were convinced that Maxima Chameleon is the stiffer material when compared to Maxima Ultragreen. Most suspected that fluorocarbon was stiffer than nylon. But when you started talking about the "premium" nylon materials, like Orvis Superstrong, Dai Riki Velvet, or Climax Freshwater, convictions were less firm.

How The Measurements Were Made
Flexible materials such as thin monofilaments don't require much force to bend them. Some writers claim to simply bend a short piece of leader material between their thumb and forefinger to gauge how stiff they are. They are deluding themselves. I estimate that the total force needed to bend a four-inch piece of 3X leader into a U-shape is about 1/100 ounce. Discriminating a 10% or 20% difference in that force is beyond the sensitivity of our fingers. The other inherent problem is that leader comes off the spool curly and no amount of stretching will remove all of that curliness. Initial curl or curvature affects the perceived stiffness.

The American Society for Testing Materials publishes many volumes of standard tests for all kinds of very flexible materials: fabric, paper, fine wire, sutures, etc. None of these tests, though, allow for initial material curl nor deal with such tiny loads as 1/100 oz.

Another approach would be to measure the stiffness to a straight pull and relate that result to the bending stiffness, which is what is really important to the fly fisher. Complications arise there, too, as materials like nylon or fluorocarbon display widely varying stiffness for small loads and large loads, so finding the effective stiffness for tiny loads is very difficult and prone to errors.

Out of desperation I had to develop a new test method. Three critical things needed to be included in this technique:

1. I had to be able to measure curly materials.
2. I could not count on accurately measuring a tiny force used to bend a piece of tippet material.
3. Results had to employ well-established engineering principles so that the inherent stiffness of the material itself could be extracted even for slight differences in length, diameter, weight, or curl in the test pieces.

Here's how it worked: Pieces of different materials were held straight out to the side (cantilever). The shape of the material was due to a combination of the curl and the sag due to the material weight, size, and stiffness. By then holding the same piece of leader so it hung straight down, it no longer sagged under its weight so the shape was due to curl alone.

To measure leader stiffness, the bent shape of the naturally curly leader is separated from the additional bending caused by the leader bending under its own weight. For more on this process, see the Proceedings of the Society of Experimental Mechanics Annual Conference on Experimental and Applied Mechanics, pp. 498-501, 2001.

I took photographs in both positions and mathematically compared the two. By separately measuring the material diameter (micrometer) and weight (precision balance), I calculated the inherent stiffness of the material. [For those interested in the details of this calculation, a scientific article is available in the Proceedings of the Society of Experimental Mechanics Annual Conference on Experimental and Applied Mechanics, pp. 498-501, 2001.]

Test Results
Overall, the inherent stiffness of materials tested is quite consistent. Most have a material stiffness of about 300,000 pounds per square inch (psi). To provide some bases for comparison, steel has inherent stiffness of about 30,000,000 psi, which is 100X as great as leader material. And, high modulus graphite fibers, like those imbedded in fly rods, have stiffnesses as high as 60,000,000 psi. So we can see that leaders truly are very flexible.

We can also compare materials. On average, fluorocarbon is about 30% stiffer than nylon. Since fluorocarbon is also about 65% more dense than nylon, sinking nymphs into heavy currents is easier. But giving them a drag-free drift is more difficult because the tippet is stiffer.

Another interesting comparison is for products from Maxima. On average, all Maxima leader materials are about 20 percent stiffer than the other nylon materials tested. But the conventional wisdom (encouraged by marketing) that Chameleon is stiffer than Ultragreen is simply not true. They both are essentially the same.

What Does This Mean?
You now have, I believe, the only objective comparison of leader material stiffness. Based on your application, you can select either a stiffer material like fluorocarbon or Maxima nylon or a more flexible material like Dai Riki or Orvis.

However, there is an important caveat: Keep in mind the effect of different diameters, because material stiffness only applies when comparing materials of the same size. And that is not just the labeled size, but the actual size. For example, if you were to compare 5X Maxima Chameleon and 5X Orvis Superstrong as it came off the spool, you would find that the Maxima leader is almost 3 times as stiff! How can that be? If Maxima Chameleon is only about 20% stiffer, how can this huge discrepancy arise? Well, the Maxima 5X leader measures 0.0075" while the Orvis is 0.0061". Diameter effects are much more pronounced that material stiffness effects.

For all things equal, the bending stiffness of a real piece of leader will vary according to a relationship that raises the diameter to the fourth power. As an example, let's compare a piece of 6X leader to 1X material. The diameter of the 6X is 0.005" and the diameter of 1X is 0.010". 1X is twice as big, or D1X = 2 D6X. Raising the factor 2 to the fourth power is 2⁴ = 16. This means that the 1X leader is 16 times as stiff as the 6X for the same material. Keep this in mind when comparing two materials. Increasing the inherent stiffness of the material by 10 percent increases the leader stiffness by 10 percent. Increasing the diameter by 10 percent increases the leader stiffness by 46 percent.

I hope that you now have a better handle on the complicated story surrounding leader stiffness. Don't trust everything that you read or hear. Don't plan to realistically discriminating tiny stiffness differences by simply bending them. Do use your micrometer to compare actual sizes when building hand-tied leaders or preparing for finicky fish. And, don't worry too much about it because the differences in stiffness or flexibility between leader materials are minute.

Graig Spolek is chair of the Mechanical Engineering Department at Portland State University. His article "Fluorocarbon Tippet Versus Monofilament" appears in the July 2003 issue of Fly Fisherman.