Fluorocarbon overview: Soft vs stiff
Stiffness = formula × process × diameter⁴. Plain PVDF is stiff; a copolymer and a different process make it soft. The same line one size heavier is much stiffer: bending stiffness rises with diameter to the fourth power, so 1.4× thicker (about 6 lb → 12 lb) ≈ 4× stiffer.
Why one fluorocarbon is soft and another stiff
| Factor | Stiffer | Softer | Basis |
|---|---|---|---|
| Resin | Plain PVDF, high crystallinity (about 45–68%) | 1–10% copolymer (e.g. HFP) added, lower crystallinity | Kureha patent: 0.30 mm line, bending modulus 1.41 → 1.14–1.17 GPa with knot strength kept |
| Double structure | A hard core carries the load | A soft outer layer knots and bends better | Seaguar Double Structure (maker claim) |
| Drawing and heat | High draw, high orientation | Relaxed in 70–98 °C (158–208 °F) water after drawing | Same patent |
| Diameter | Heavy sizes | Light sizes | Bending stiffness ∝ diameter⁴ |
| Temperature | Stiffer in the cold | Softer when warm | PVDF material behaviour |
Soft vs stiff, trait by trait
| Soft FC | Stiff FC | |
|---|---|---|
| Handling, memory | Supple, low memory | Stiff, more memory |
| Spinning reel | Easy | Springs off the spool, wind knots |
| Small-lure action | Natural | Can be deadened |
| Abrasion | Lower (small-sample test) | Higher |
| Sensitivity | A little softer | More direct feel (tester opinion, not instrument-measured) |
| Hookset | A bit more stretch, some cushion | Less stretch at low load, more direct |
| Tangles | Rigs tangle more | Runs straight: wraps cover less, leaders tangle less |
| Knot strength | Seats easily | Bigger knot loss (about 71–76% knotted, measured) |
| Examples | Seaguar InvizX, Tatsu; Sunline Super FC Sniper | Sunline Shooter; Toray SuperHard; Seaguar AbrazX |
After the load: stretch, recovery, "the corkscrew"
| Load | What happens | Soft FC | Stiff FC |
|---|---|---|---|
| Everyday load (well below break) | Elastic stretch; most of it comes back | Stretches a bit more, keeps a bit more (about 2% at 3 lb) | Stretches less, keeps less (0–1% at 3 lb) |
| Overload: yanking a snag, a brutal hookset | Past the yield point: permanently longer, thinner, weaker, curled where it yielded | Anglers widely find it "stretches and comes back" better | Anglers widely report thin stiff FC corkscrews after a hard pull, and weakens and breaks |
| What to do | — | Cut the section that was pulled hard and retie | Same; especially with light stiff FC |
Measurements only cover everyday loads: at 3 lb, stiff FC kept LESS permanent stretch than soft FC. No soft-vs-stiff overload test was found; the overload row is angler experience.
Measured at 3 lb (TackleTour 2007, historic samples)
| Line | Type | Rating · diameter | Stretch under load | Left after unloading |
|---|---|---|---|---|
| Sunline Shooter | Stiff FC | 14 lb · 0.32 mm | 6.3% | 0% |
| Toray SuperHard | Stiff FC | 14 lb · 0.32 mm | 7.7% | 1.1% |
| Maxima Fluorocarbon | FC | 12 lb · 0.31 mm | 7.4% | 1.1% |
| Gamma Edge | FC | 10 lb · 0.31 mm | 11.5% | 2.1% |
| Seaguar InvizX | Soft FC | 10 lb · 0.30 mm | 13% | 2.2% |
| Berkley Trilene XL | Nylon (reference) | 12 lb · 0.32 mm | 9.4% | 0% |
- 3 lb is 30% of a 10 lb label but only 21% of a 14 lb one: different ratings are not equally loaded. After a 3-hour soak, InvizX and Gamma kept about 3%.
- At break, fluorocarbon and nylon both stretch roughly 20–30% in total (VARIVAS: FC 23–30%, nylon 25–35%): "FC doesn't stretch" is true only at low load.
Soft or stiff by technique
| Technique | Choose | Common lb |
|---|---|---|
| Spinning finesse leaders: drop shot, Ned, Neko, wacky | Soft | 4–10 lb |
| Spinning with FC as the main line | Soft | 4–10 lb |
| Jerkbaits, crankbaits (action, depth) | Softer | 8–12 lb |
| Baitcaster jigs, Texas rigs, flipping | Stiff | 12–25 lb |
| Carolina and drop-shot leaders (fewer tangles) | Stiffer | By the main line |
| PE leader · open-water finesse | Soft | PE number × 2.5–3 |
| PE leader · cover | Stiff | PE number × 3–4 |
Sources: Kureha patent US7172810B2 · Seaguar technology · TackleTour stretch test · TackleTour Shooter · VARIVAS line guide · Soft vs hard FC (Japanese)
Fluorocarbon overview
Fluorocarbon in six tables: soft vs stiff, main line or leader, diameter and abrasion, sinking and visibility, colour, knots and care.
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