Fluorocarbon vs. Nylon

“Monofilament” is a term of art used to describe extruded, single-strand fishing line made from a variety of different plastics. Monofilament leaders and tippets are now made from three distinctly different plastic materials: nylon, fluorocarbon and bioabsorbable polymer. Each material offers advantages and disadvantages compared to the others.

The amount of marketing drivel that has been published extolling the virtues of fluorocarbon monofilament over nylon is almost beyond belief. While some of it is undoubtedly true, most is based on the properties of the two materials and their theoretical differences, rather than practical experience in using them under a wide variety of fishing conditions. The purpose of this article is to bring fly anglers up to speed on just what those advantages and disadvantages really amount to in a “real world” setting.

Nylon and fluorocarbon (polyvinylidene fluoride, or PVDF) monofilament materials have been around for quite a while, but bioabsorbable polymer monofilament is brand new to the fishing industry. Bioabsorbable polymer monofilament was originally developed in the 1970s for use by the medical industry as “dissolving” stitches, and cost over $5.00 per yard at the time. Bioline, of Portland, Oregon (recently purchased by Denver-based Wright & McGill) started marketing bioabsorbable polymer monofilament fishing line in July, 2008, and the product line is being expanded to include fly-fishing leader and tippet material. If you’re wondering what the big deal is with bioabsorbable polymer monofilament, read on.

Environmental Impact

How many times have you lost a monofilament tippet—or an entire leader—or inadvertently dropped a piece of waste monofilament line into the water? If you’re like the rest of us, the answer is “lots.” Even if you religiously store used monofilament line in a Fishpond PIOpod and dispose of it properly in the trash, it’s still going to wind up back in the ecosystem—either in a landfill or dumped at sea.

First introduced by DuPont in 1939, millions of miles—perhaps tens of millions of miles—of nylon monofilament fishing line have been produced in the last 70 years, and every inch of it is still sitting out there somewhere in the ecosystem . . . and will be for at least the next 530 years. That’s right, whether buried underground or floating around in our rivers, lakes and oceans, nylon monofilament takes 600 years to biodegrade.

Why is this important? Each year, thousands of animals and countless boat propellers become entangled in discarded monofilament line. Shorebirds, bald eagles, sea turtles, and marine mammals can starve to death, lose limbs, or drown because of entanglement in monofilament fishing line. Since it’s usually clear or light in color, monofilament line is difficult for birds and mammals to see, making it easy for them to get wrapped up in the stuff. One in five manatees rescued between 1980 and 1999 were entangled in monofilament line, and God only knows how many others died before they could be rescued. In one study, 38% of green turtles that washed up dead in Florida had eaten monofilament line, and discarded or broken off monofilament fishing line has been identified as one of the leading causes of infant dolphin deaths. Even humans are affected—every year human divers drown as a result of entanglement in monofilament fishing line (usually the heavier commercial-fishing variety).

While it may be difficult to conceive of the havoc that millions of miles of discarded nylon monofilament line will cause over the next 530 years, one can only imagine what those consequences will be over the next 4,000 years. That’s how long it takes for fluorocarbon monofilament to biodegrade. For all practical purposes, fluorocarbon monofilament never biodegrades.

Bioline, on the other hand, fully biodegrades in just five years, and in the process breaks down to nothing more than a minimal quantity of carbon dioxide and water. If there’s a winner here, it’s not nylon or fluorocarbon. The five-year life span of Bioline still has the potential to cause harm, but it certainly pales in comparison to that of nylon and fluorocarbon monofilament. 

Cost

Plain old nylon monofilament is the least expensive of the three monofilament leader and tippet materials, and the clear winner on this measure. Thirty- to 33-yard spools of nylon monofilament tippet material run from about $2.95 to $5.95, depending on the brand, diameter and where you buy it. The cost for a single knotless, tapered nylon leader falls into the same price range.

Knotless, tapered fluorocarbon leaders go for $5.99 to $9.99 each, while 30- to 33-yard spools of fluorocarbon tippet material are priced from $8.99 to $15.99.

Bioline tippet material sells for $9.99 in 30-yard spools, making it price competitive with fluorocarbon. Bioline does not yet offer knotless, tapered leaders, but they do make leader material for tying your own, priced at $8.99 per 30-yard spool.

Specific Gravity

It’s been said that the most common reason why even half-smart trout reject a dry-fly offering is because they see the squiggly outline of the leader on the water’s surface. Makes sense to us. Why else would every fly shop be selling those little squeeze bottles of “leader sink” that work for a while before they wash off? It sure would be nice if leaders and tippets sank all by themselves.

The density of a material, compared to that of water, is expressed as its specific gravity. To keep things simple, whoever developed the specific gravity scale—some Englishman, no doubt—assigned water a specific gravity of 1.00. Materials with a specific gravity of less than 1.00 are lighter than water, and will float. Materials having a specific gravity in excess of 1.00 are heavier than water, and will sink . . .  theoretically, at least.

The actual blend of polymers used to produce “nylon” varies somewhat, but the nylon formulations used to make monofilament leaders and tippets generally have a specific gravity in the range of 1.05 to 1.10, making them just slightly heavier than water. To put those numbers in perspective, tungsten—used in high-density sink tips—has a specific gravity of 19.25.

Being slightly heavier than water does not mean that nylon monofilament is going to sink, at least not quickly or very well. Surface tension—where the water’s surface behaves like an elastic film—must be broken before an object will sink. A object’s density and contact angle with the water’s surface are the two most significant variables in its ability to break surface tension and sink, and the “just slightly heavier than water” specific gravity and zero contact angle (i.e., laid out flat) of a nylon monofilament leader or tippet are not sufficient to do it most of the time. If pushed or pulled under the surface by a weighted fly or roiling current, nylon monofilament will sink . . . but very, very slowly.

Fluorocarbon has a specific gravity in the range of 1.75 to 1.90. Tungsten it ain’t, but it is significantly more dense than nylon. But is it sufficiently dense to quickly and reliable break surface tension and sink all by itself, even at zero contact angles, and even in the smallest diameters? No, it’s not. Our testing reveals that most brands of fluorocarbon tippet material in 0X to 8X diameters are no better than nylon at breaking surface tension and sinking on their own. Larger diameter fluorocarbon materials do demonstrate a slightly better ability to break surface tension without the assistance of current or other external influences, but for practical fishing purposes fluorocarbon has little benefit over nylon on this measure.

Water Absorption

Nylon monofilament is a lot like spaghetti—it absorbs water in copious quantities. Trying to pull a piece of dry spaghetti apart end to end is tough, but as soon as it gets cooked (i.e., it has absorbed a bunch of water) it pulls apart with ease. That’s an extreme example, but you get the picture.

In reality, nylon monofilament will absorb up to about 10% of its weight in water. Water absorption is a mixed blessing. On the upside, nylon monofilament that has absorbed water becomes more limp and supple, and makes knot tying easier. On the downside, water-logged nylon monofilament swells, increasing its diameter, reducing its break strength by about 20% (i.e., 10-pound test becomes 8-pound), and increasing its elongation (stretch) by 25% to 30%.

Fluorocarbon monofilament, however, is basically impervious to water. Depending upon the formulation, it absorbs less than 0.05% of its weight in water, with the result that none of its physical properties change after a prolonged soaking. The diameter, break strength and elongation of wet fluorocarbon monofilament remain essentially the same as dry fluorocarbon—but so does its stiffness, resulting in no appreciable reduction in line-coil memory after prolonged use. If you can live with more pronounced memory, fluorocarbon gets the nod here.

Ultraviolet Degradation

Nylon monofilament is particularly susceptible to ultraviolet radiation. The same component of sunlight that causes sunburns, UV radiation quickly degrades nylon—principally through oxidation—resulting in significant loss of strength over time. How much time? As Hamlet would put it, “Ay, there’s the rub.”

Tests show that nylon’s loss in strength can be as great as 20% of its original strength in the first 100 hours of exposure to UV radiation, with an additional 20% loss in strength over the next 100 hours of exposure. Fluorocarbon, on the other hand, is completely unaffected by UV exposure. And since it’s impervious to water as well, there’s no chance of compounding the problem with additional degradation due to water absorption.

The 100 hours of daylight fishing it would take to degrade the strength of your nylon monofilament leader or tippet by 20% translates into 12.5 full 8-hour days on the water. The vast majority of tippets don’t last a fraction of that time, and tapered leaders with progressively higher break strengths as they are trimmed back are of much less concern, so what’s the big deal with UV degradation?

Probably not all that much for most anglers most of the time, but consider this. When you combine a significant loss in strength due to UV degradation with a 20% additional loss of strength due to water absorption, the risk of losing a good fish becomes a real possibility unless you regularly replace old (i.e., UV-exposed) and/or waterlogged nylon monofilament tippets and leaders.

Wet Knot Strength

The only knots that really matter for anglers are the wet ones, and nylon monofilament has a slight edge over fluorocarbon on this measure. Tests with a surgeons knot, lubricated before cinching, and then immersed in freshwater for 20 minutes, demonstrate that nylon monofilament breaks at the knot at an average of about 80% of its rated break strength. Fluorocarbon isn’t far behind at an average of about 75% of rated break strength. These numbers will vary somewhat by diameter and brand of material. 

While the difference between nylon and fluorocarbon wet-knot break strength may be statistically significant, the “real world” difference is minimal at best. In fact, for most anglers the wet break strength of their knots is more a function of the quality of the knot than the material with which it is tied. Because fluorocarbon is harder than nylon, it is especially important to ensure that fluorocarbon knots are tightly cinched and fully seated.

Stretch

We won’t bore you with the science of elasticity and plasticity, but the bottom line here is that dry nylon and dry fluorocarbon monofilaments both stretch under load, and the amount of stretch they exhibit is roughly equal. But that’s where the similarities end.

Nylon monofilament is more elastic than fluorocarbon, and as a result it is better able to recover from stretch when the load is removed. For example, a 10-foot length of a particular brand and diameter of nylon monofilament may stretch to a length of 11 feet (10% elongation) under a given load, but when that load is removed it recovers to a length of 10.2 feet, meaning that its permanent elongation, as a percentage of original length, is only 2%. 

Being less elastic that nylon, a similar length and diameter of fluorocarbon monofilament may stretch to the same 11-foot length when subjected to the same load, but when the load is removed it only recovers to a length of 10.8 feet, so its permanent elongation is 8%. In essence, fluorocarbon monofilament stretches to nearly the full extent of its permanent elongation upon the first loading, whereas nylon stretches and recovers repeatedly as loads are applied and removed. The relative elasticity of nylon over fluorocarbon may be seen as a benefit in some situations, as it can act as a shock absorber that dissipates the energy of a hook set.

In the examples above the materials were dry, but what happens after they have been thoroughly soaked? The nylon monofilament absorbs up to 10% of its dry weight in water, whereas the fluorocarbon monofilament absorbs almost no water. As a result, the elasticity and plasticity of the fluorocarbon monofilament is essentially unchanged, whereas the nylon material now exhibits even more elongation—both temporary and permanent—when wet than it did when dry. Is this a bad thing? Well, it can be, as the now permanently stretched section of nylon monofilament is significantly smaller in diameter. Put another way, your 6-pound nylon tippet just became a 4-pound tippet, never to become a 6-pound tippet again. Just one more reason to regularly replace used nylon tippets and leaders.

Abrasion Resistance

The surface of fluorocarbon monofilament is harder than that of nylon, making it substantially more resistant to abrasion. For our money, the greatly increased abrasion resistance of fluorocarbon monofilament is its single most valuable attribute. In years of fishing for fresh- and saltwater species all over the world, we’ve seen countless examples of the abuse that fluorocarbon leaders and tippets can stand up to—jagged rocks, coral heads, sharp gill plates, and lots of teeth. On this measure, the theoretical and the practical come together, and fluorocarbon is the standout winner.

Refractive Index

The refractive index of a material is a measure of how much the speed of light is reduced as it passes through the material. Water has a refractive index of 1.33, meaning that in water light travels about 75% of the speed it does in a vacuum. The average refractive index of nylon monofilaments is about 1.58, meaning that when passing through nylon light travels at about 63% of the speed it does in a vacuum. Fluorocarbon has a refractive index of 1.42, meaning that when passing through fluorocarbon light travels at about 70% of the speed it does in a vacuum. Since the refractive index of fluorocarbon is closer to that of water than is the refractive index of nylon, fluorocarbon is theoretically the less visible material when immersed in water. That’s the science, and we hope it does more for you than it does for us.

We’ve tried for years to come up with a practical test of the comparative visibility of fluorocarbon and nylon monofilaments in water, without any demonstrable success. We’ve immersed fluorocarbon and nylon tippet materials of similar diameters side by side in water—in water glasses, sinks, aquariums and saltwater shallows—in depths from a couple of inches to over a foot. We’ve even tried photographing them under water, but we’ll be damned if we can see a difference. Both materials appear equally visible against a wide range of backgrounds.

That being said, the only view that counts is the fish-eye view, and in many years of using both nylon and fluorocarbon leaders and tippets in every conceivable fishing situation it is our subjective impression that fluorocarbon produces more hook ups than nylon. That conclusion is based on nothing but observation (albeit, thousands of them) any is completely lacking in any empirical data. Nonetheless, fluorocarbon appears to be less visible to fish, and for that reason alone it’s worth using, at least under certain conditions—like on the flats—where any degree of added stealth is a clear benefit.

Relative Break Strength

This one is going to require a bit of explanation to make the point. Because there is no industry standard on how the break strength of monofilament tippet material is rated, manufacturers express these values in a couple of different ways: “rated” break strength and “average” break strength. Both methods undoubtedly involve testing on the part of the manufacturers, but since none of them distinguish between “wet” and “dry” break strengths we assume that all such testing is performed using dry materials. 

It’s pretty clear that for any given diameter—and regardless of which rating system is used—dry nylon has a significantly higher break strength than dry fluorocarbon. How much higher? In the case of Climax products (listed as “rated” break strength), the average difference is 13%; for Scientific Anglers products (using “average” break strength), it’s 9%. Across both brands and rating systems, the average difference is 11%. Sounds fairly conclusive, huh?

Not really. If you use this stuff for fishing like we do, it’s going to get wet. And what happens to nylon monofilament when it gets wet? That’s right, it absorbs water . . . lots of water . . . to the tune of 10% of its dry weight, in the process losing up to 20% of its dry break strength. As we’ve learned, fluorocarbon is essentially impervious to water—absorbing less than 0.05% of its dry weight—with zero effect on its dry break strength. After a half hour or so of fishing, nylon’s break-strength advantage has been negated by water absorption, and as immersion time increases, fluorocarbon quickly becomes the front runner. 

What About Bioline?

Because Bioline is so new, there is very little technical information available relating to its performance characteristics, and we’ve been unable to obtain any product samples to conduct our own testing. At this point all we can do is pass along the available marketing hype—something we typically refuse to do—but because Bioline shows so much promise for our sport, we’re making an exception. So here it is, right off the their website (www.biolinefishing.com):

“The inherent advantages of Bioline’s chemistry are not limited to being biodegradable. Unlike nylon monofilament, Bioline does not absorb water. Its strength and stretch does not change. Bioline provides excellent knot strength and is highly UV and abrasion resistant. With low-memory and a silky smooth exterior, Bioline is an exceptional casting line on both spinning and casting reels alike. Clear in color, Bioline provides stealth in fresh and saltwater applications. A cornerstone in Bioline’s biofilament development was providing a functional temporal window within which the angler can depend upon 100% strength. If kept sealed in its original package, Bioline has a five year shelf life. Once spooled on a reel Bioline will suffer no degradation in strength or performance for a period of 10 to 12 months. Tournament anglers, fly anglers and avid anglers who change lines regularly will see absolutely zero loss of performance. In fact, if casual anglers change line only at the beginning of each season, as is also recommended for conventional monofilaments, they’ll receive 100% performance from Bioline.”

We’re on the short list at Wright & McGill for some Bioline product samples, and just as soon as we get them—and Wright & McGill gets up to speed on their Bioline product line—we’ll bring you a definitive review. In the meantime, we’d love to hear from any readers who have had the opportunity to try Bioline.

The Bottom Line

Until the jury returns its verdict on Bioline, we’re left with choosing between nylon and fluorocarbon monofilaments for our leaders and tippets. On most measures, the performance characteristics of both materials are close enough to make a “one-or-the-other” decision equivocal at best.

Both materials are environmental time bombs, and the fact that nylon biodegrades 3,400 years sooner than fluorocarbon does little to forgive its 600-year environmental “shelf life.”

As I tell my wife on a nearly weekly basis, “Any dumb #?*@&% can spend money,” and considering that nylon monofilament leaders and tippets are priced at roughly half the cost of their fluorocarbon counterparts, nylon is the clear value leader.

Less clear are the relative performance advantages of the two materials. Nylon gets the nod on wet knot strength, but not by much, and demonstrates no clear advantages over fluorocarbon on any other measure. Neither of them sink very well on their own, and both materials stretch to about the same extent (although in different ways). Nylon has a higher dry break strength, but after a thorough soaking it cedes that advantage to fluorocarbon. Even though we “feel” that our hook-up rates are higher with fluorocarbon, both materials appear equally visible under water. So what’s left?

The three “biggies” for us are water absorption, UV degradation and abrasion resistance, and fluorocarbon holds the high ground on all three measures by a wide margin. Water absorption results in nothing but negative consequences, and fluorocarbon’s zero water absorption avoids them all. Ditto with UV degradation. But our biggest “biggie” is fluorocarbon’s greatly increased resistance to abrasion.

So which material do we use for our leaders and tippets? We use both. For any “mission critical” application where fish absolutely have to be landed for photography, we use fluorocarbon leaders and tippets exclusively—the cost be damned. To do anything else would be a “penny wise and pound foolish” proposition. For general dubbing around on our local trout fisheries, we use nylon with greater frequency.

What it really comes down to is cost-benefit analysis. When you’ve just dropped five grand on a flats-fishing trip to the Yucatan, screw the cost and bring plenty of fluorocarbon. When you’re just out for an evening of throwing dry flies at stocked trout, save a buck or two and go with nylon. After all, any dumb #?*@&% can spend money.

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Bill Battles is FFA’s executive publisher, and has been know to swear when he breaks off a fish. Real-world testing has shown that he swears less when using fluorocarbon.