Fluorocarbon fishing line is a single strand of polyvinylidene fluoride, PVDF, and three properties set it apart from nylon monofilament: it refracts light almost like water does, it sinks, and it hardly absorbs water. Seaguar, which invented it in 1971 under its parent company Kureha, gives the refractive indices on its FAQ: water 1.33, fluorocarbon 1.42, nylon 1.62, which is the whole reason a fluorocarbon leader is harder for a fish to see. It stretches less than mono, resists abrasion better, and lasts longer on the spool. It also costs three to five times as much, sinks a topwater lure, and fails at the knot if the knot is tied dry. Below: the properties measured against mono and braid, where fluorocarbon wins and loses by technique, the knots, and how to buy it.
Fluorocarbon bends light almost the way water does. Under the surface, that is the difference between a line and no line.
The properties, measured
| Property | Fluorocarbon | Monofilament | Braid |
|---|---|---|---|
| Refractive index (water 1.33) | 1.42 | 1.62 | Opaque |
| Sinks or floats | Sinks; Seaguar’s demonstration drops 30 cm in 15 seconds against 40 for nylon | Neutral to slow sinking | Floats |
| Stretch | 10–15% | 25–30% | About none |
| Diameter at 20 lb | 0.015–0.016 in (0.38–0.41 mm) | 0.016–0.018 in | 0.009–0.010 in |
| Abrasion resistance | High; harder surface | Moderate | Low; frays on shell and rock |
| Water absorption | “Absorbs very little water” | Absorbs, and weakens wet | None |
| Memory | Moderate to high; stiffer than mono | High | None |
| Life on the spool | 1–2 years | 3–6 months in sun | 2–5 years |
| Price per yard | $0.05–0.15 | $0.01–0.03 | $0.04–0.10 |
| Knots | Wet, and pull slowly; Palomar, improved clinch | Ties easily | Needs braid knots and a leader knot |
The diameters are Tackle Village’s measurements of Berkley Vanish against Trilene and SpiderWire; at 10 lb fluorocarbon and mono are the same 0.011 in, and fluorocarbon’s edge in thinness at a given strength is small. Its edges are invisibility, sink rate, sensitivity and abrasion.
Where it wins, and where it loses
Matt Allen’s line guide at Tactical Bassin and the Tackle Room’s material guide reach the same verdicts, technique by technique.
| Technique | Fluorocarbon? | Why |
|---|---|---|
| Leader on braid, any technique | Yes, the standard use | Invisibility and abrasion resistance at the lure, braid’s strength and casting behind it |
| Jigs, Texas rigs, shaky heads in clear water | Yes, as main line, 12–20 lb | Sinks with the bait, low stretch feels the bottom and the bite |
| Drop shot | Yes, 6–10 lb | Sinks and keeps the bait down; invisible to pressured fish |
| Crankbaits and jerkbaits | Yes, 10–15 lb | Gets the lure deeper than mono; enough stretch left to keep trebles pinned |
| Finesse for trout and smallmouth | Yes, 4–8 lb, often as a leader | Clear water, wary fish |
| Topwater: poppers, walkers, frogs | No | “Fluorocarbon sinks. Use it for topwater and it will drive you insane,” Allen writes; the line drags the nose under |
| Spinnerbaits, chatterbaits in stained water | Either | Fish cannot see the line anyway; mono is cheaper and casts better |
| Punching and flipping heavy cover | No; braid | Fluorocarbon’s abrasion resistance is not braid’s strength at 50–65 lb |
| Trolling, circle-hook bait rigs, beginners | No; mono | Stretch cushions the take; the price does not pay off |
| Frozen-water fishing and very cold days | Careful | Fluorocarbon stiffens and coils in the cold; mono or braid-to-short-leader |
Where it came from, and what “100% fluorocarbon” means
Kureha, a Japanese chemical company, made the first fluorocarbon fishing line in 1971 and sells it as Seaguar; for twenty years it was a leader material for saltwater anglers who could afford it, and it reached bass fishing as a main line in the 1990s when softer formulations made it castable on a baitcaster. Today most of the big brands buy their fluorocarbon from a handful of Japanese extruders and finish it themselves. The label matters: “100% fluorocarbon” is a solid PVDF line with the properties in the table, while a “fluorocarbon-coated” line is nylon monofilament with a thin fluorocarbon skin, which sinks a little better than plain mono and is otherwise mono, at a mono price. The coated lines are honest products for crankbaits and spinnerbaits; they are not what a drop-shot angler means by fluorocarbon.
The knots, and why they fail
Fluorocarbon is harder and stiffer than nylon, and a knot pulled tight dry heats and burns the line at the wraps; the failure shows as a curly pigtail on the end of the line where the knot used to be. Wet the knot with saliva or water, pull it down slowly and evenly, and pull the tag and standing line rather than yanking. The Palomar is the strongest and simplest for hooks and jigs on fluorocarbon up to about 20 lb; the improved clinch works and is easier on heavier line; for joining a fluorocarbon leader to braid, the FG knot is the slimmest and strongest and the double uni the easiest. The Palomar knot, improved clinch and FG knot pages show them; the braid to mono knot page covers the leader join.
Buying it
- Leader material or main line. Leader spools (25–50 yd) are harder, more abrasion-resistant and dearer per yard; main-line spools (200 yd) are softer and cast better. Buy the one for the job.
- Pound test by technique, from the table: 6–10 lb finesse, 12–17 lb jigs and Texas rigs, 10–15 lb crankbaits, 15–25 lb leaders for inshore salt.
- Buy less, more often. Fluorocarbon lasts longer than mono, but 200 yd on a spool is still two seasons; a bulk 1,000 yd spool goes brittle before it is used up.
- Spool it under tension and fill to 1/8 in below the lip; fluorocarbon’s memory throws coils off an overfilled spool. The how to put fishing line on a reel page has the steps.
- Keep it out of the sun. UV degrades it slower than nylon but still degrades it; a spool on the dashboard is dead in a summer.
Related
The fluorocarbon vs monofilament page argues the two head to head with the measurements; the monofilament fishing line page makes mono’s case; the fishing leader page covers the leader lengths and the wire alternative; and the line hub has the whole picture. For what to tie on the end, the Texas rig and drop shot pages are where fluorocarbon earns its price.