Simplifying the Great Debate: Fluorocarbon vs. Nylon: INVISIBILITY

I read and hear conversations all of the time debating the advantages & disadvantages of nylon monofilament vs fluorocarbon monofilament for leaders and tippet.  Once again, the real question is:  How much of the stuff you hear/read on this topic is truth versus marketing hype?  Let’s see if we can sort some of this out.

TRUTH:  Fluorocarbon has a closer refractive index to water than that of nylon.

Yes folks this is a cold hard scientific fact.  Refractive index essentially refers to a number indicating  how much the speed of light is reduced in a given medium.  I just got a headache from typing that.  Water has a refractive index of 1.3330.  Fluorocarbon has a refractive index of 1.42.  Nylon monofilament refractive indices range from 1.53-1.62.  BUT, does that really mean fluorocarbon is invisible in water?

MYTH: Fluorocarbon is nearly invisible to fish in water.

Clear back in 2001 a guy named Jeff Thomson wrote an article called, “Mathematical Theory of Fishing Line Visibility”.  Now, I can’t find that this is an actual peer reviewed published article, but I have read the presentation he did on the topic and it is pretty good.  He essentially breaks down how light refraction, reflection, and scatter in water works from a mathematical equation perspective and then applies the properties of water and fluorocarbon in those equations.  It’s painful to read if you do not have a science and research background (and even then, it’s pretty painful).  He ultimately concluded that considering all of the variables involved, in reality, fluorocarbon monofilament is not “invisible” in water.

Anecdotal evidence (a limited selection of examples which support or refute an argument, but which are not supported by scientific or statistical analysis) by many fisherman suggest that, yes fluorocarbon is less visible to fish than nylon monofilament.  So, is this true?  Maybe…

A lot of folks have reported many types of tests to quantify this (non-scientific tests, but interesting nonetheless).  People have put lengths of same diameter nylon and fluorocarbon in glasses of water, aquariums, in lakes and rivers, and looked at them and photographed them.  The majority of those folks report they can’t see a difference between the two.  Of course they all admit they are not fish under water looking at the materials with the naked eyes of fish.

My own anecdotal evidence suggests that in clear water, steelhead most certainly see fluorocarbon monofilament line when it drifts towards them and they move out of the way from the offering (no matter what it is) well in advance of it ever getting to them.  While I cannot write a peer reviewed scientific paper based on my observations, I’m comfortable saying, in gin clear water….fish can see fluorocarbon monofilament line.

YET, I do construct my leaders from and use tippet material made of fluorocarbon.  Why is that if it is not invisible and certainly costs more?  For me it’s simple.  I guide clients with varying degrees of experience.  And fluorocarbon does give me some advantages. 

Fluorocarbon has higher tensile strength at smaller diameters than nylon.  I want to give clients every advantage I can, knowing full well when they are with me they are in the middle of a big learning curve on how to catch steelhead on the fly rod.  So, it is true, fish are less spooked by smaller diameter line and if I can use a smaller diameter line that is stronger to help a client get a fish to hand, it’s a win win. 

Once someone is comfortable with proper presentation of offerings and how to land a big crazy fish on fly gear, many of the reported advantages of fluorocarbon may not be as significant.  From my perspective, I have a very limited amount of time to spend with any given client to cover a ton of material and get some fish in their hands.  In that setting, fluorocarbon limits some of the issues with presentation error and helps a little with not breaking off fish when making common mistakes fighting and landing these big fish. 

From my personal fishing perspective, at the end of the day, hooking fish still comes down to precise PRESENTATION PRESENTATION PRESENTATION.  In my opinion, the visibility of the line plays very little role in whether I hook fish.  And there a a multitude of other ways we spook fish and shut down a bite before we ever get out lines in the water.  In previous articles we have discussed that fish see a lot in an out of the water that does not even relate to line visibility.  And this does not even account for things we do unknowingly that disturb a run before we even get close to it.  We would be hard pressed to narrow why we are not catching fish down to the visibility of the line we use.  But it can be a piece of the overall picture that also should not be neglected.

To me, it’s more of an issue of making the right kind of presentation in low gin clear water than having an invisible line.  For example, swinging an offering down in front of fish presents only the offering to the fish (not the line), where drifting an offering does tend to present the line and offering at the same time.  And in the case of Steelhead Alley steelhead, they get educated to line drifting at them pretty quickly from the moment they enter the tributaries.

I’ll discuss other topics within this specific debate in upcoming articles.  Until then, if you’re gonna be in northeast Ohio or northwest Pennsylvania on business and want to spend a day on the water or you are local and just want to work on some aspect of your steelhead game…call me!  LET’S GO FISHIN’!