Line Hacking

Line Hacking

With a few simple techniques, and someone else's curling iron, you can build welded loops and any fly line you might need.

  • By: Zach Matthews
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“SNICK!” I felt—more than heard—the sound, as
the tension on my fly line suddenly gave way, sending it rebounding in puddles through my guides and nearly toppling me over in my boat. The striped bass I had been fighting thrashed once, then submerged and was gone, taking fly and leader with it. My line had failed not on the terminal knots, but instead on the line-to-leader connection. It turns out your standard trout nail knot is not really strong enough to handle stripers, at least not for long.

That was when I started trying to find a better way to rig my terminal tackle. I had been nail-knotting Amnesia monofilament onto my lines for years, always to serve as a short leader butt and always with a perfection loop tied in so I could switch leaders easily with a loop-to-loop knot. That system works well, unless you’re fighting big fish or you try to reel the knot into the tip-top. Nail knots work by clamping onto the coating of the line, and if that coating slips, so will the knot.

Line makers went a long way toward alleviating these problems when they began putting “welded” loops on lines a few years ago. Made in the factory, these loops rely on a welded bond in the PVC coating (the material in the “jacket” of most lines, in industry parlance). This loop is especially resilient because PVC can stretch. In fact, according to sources inside the industry’s line-testing labs, welded loops are almost always stronger than the core breaking strength of the line itself.

The only problem with welded loops is that they can wear out. And manufacturers have largely stopped including welded loops on the backs of lines for cost reasons. Conventional wisdom says welded loops must be made at the factory. Conventional wisdom is wrong.

Working on a tip from an industry insider, I Procured a standard ladies’ flat iron originally designed for straightening hair (15 bucks at a discount store). These irons, which have a temperature setting in the range of mid-400 degrees Fahrenheit, turn out to be the perfect tools for heating and pressing welded loops into fly line without burning or scorching the PVC.

The procedure is extremely simple: Cut the square tip off the line on a sharp bias, producing a long point; this will make the coating lie down better once it is welded. Double your line over, typically leaving about a one-eighth-inch to one-quarter-inch loop, and giving yourself at least an inch of line to fuse together. Pre-heat your iron. Place your loop in something to hold it (a plastic wallboard anchor or a pen cap), then gently heat and tap the tag into the running line using your iron. The heat will liquefy the coating to a gel-like consistency. I find it easiest to press the line together tightly with my fingers while it is soft, then let it cool. Once it is rigid again, use the flat iron to smooth and shape the coating, repeating the process as necessary to make a smooth, rounded bond.

Alternatively, you can also use clear heat-shrink tubing to “pin” the loop while you heat it with the iron. The clear tubing allows you to see the weld to ensure it is properly fused, while the tubing itself serves as a form to keep the bond rounded. When you are done, you can either cut the tubing off (cosmetically preferable), or leave a section for reinforcement purposes. Heat shrink also allows you to make longer welds, for maximum strength—most appropriate for big-game applications, like shooting heads for steelhead. Some anglers also use heat guns instead of hair irons with heat-shrink tubing; this method works well, but doesn’t allow you to apply as much pressure as with the iron and may not form as strong a bond.

Our manufacturing sources have cautioned that fly lines do not carry a warranty except against manufacturing defects. Obviously, welding one’s own loops carries some risk (you want to be sure you don’t accidentally nick the body of the line with the iron while it is hot, or you’ll create a weak spot). Of course if you’ve already worn out one loop, you have nothing to lose by making another. If you fail, you can always go back to the nail knot.

I found the technique to be surprisingly easy. By my third attempt I was ready to strength-test the system. Using 5-weight fly line with a rated core breaking strength of 20 pounds, I was able to apply more than 20 pounds of pressure to the line three times before the weld finally failed. [Check out the video at – Ed.] On one test, the line itself broke before the weld. Curious, I repeated the test using a standard nail knot with 20-pound-test mono, and also with an Albright knot. The nail knot failed at 10 pounds of pull force. The Albright did slightly better, at 12 pounds. I was shocked to discover that welded loops are up to twice as strong as the systems I had been using for years!

Some caveats are in order. Welded loops do not appear to be possible with monocore or some sinking lines, at least not at home. With monocore lines, the core is made of monofilament, which warps and coils when one applies heat. Meanwhile most sinking lines—at least in lighter line weights—simply do not seem to have a thick enough “jacket” to provide you with enough material to make a strong bond. On the other hand, the heavier one goes with floating fly lines—for example, 8- or 10-weight lines—the stronger the welds get.

And: You should also be careful to work in a well-ventilated area or even outside. Vaporized PVC is a known health hazard, and although the volume of plastic fumes put off by briefly fusing fly-line welds is very small, it’s still not be a good idea to inhale burning plastic.

The beauty of being able to weld fly lines at home is that you can make almost anything you want. One of the rivers I fish most often is characterized by rocky shoals between high banks, almost cliffs in some places, thick with rhododendron and other line-grabbing vegetation. The area is too tight for most backcasts, but it’s perfect for single-hand Spey-casting. The fish there are your standard trout, as well as shoal bass up to a couple of pounds—perfect 5-weight targets. Unfortunately, no one makes a Skagit head system for single-hand Spey-casting in a 5-weight. So I decided to make one myself.

Using the back of an old 5-weight line as a running line, I first welded loops in each end, giving me about 60 feet of skinny, shootable floating line. Then I took an old 8-weight bass taper that had sat in a drawer for nearly a decade. Skagit lines are characterized by very heavy front heads; the mass of the head carries the running line far away even with choppy single-hand Spey or rollcasts. I cut the line 30 feet from the tip, and welded another loop. Welded loops slide well through guides, but to ensure maximum strength at the “hinge” point, I also used heat-shrink tubing and made a longer weld. I then welded a final loop on the front of the old bass taper and voila! I had myself a perfectly serviceable 5-weight Skagit system.

The proof was in the pudding. Using my new line, I was able to work my way from rock to rock, making short, controlled rollcasts behind each shelf and dropoff, picking up both trout and shoal bass left and right.

Whether you’re repairing a broken welded loop or making a custom shooting-head system, or you’d just like to get a little more use out of those old lines sitting in a drawer, the tools you need are as close as your local beauty supply shop. So get creative, come up with something new, and who knows—maybe your taper will be the next big thing in fly-casting.


Line Weld

  • Cut the square end of your line to a sharp point, to better make the end lay down when you fuse it.
  • Pre-heat your iron.
  • Double the line over so that you have a loop of about one eighth to one quarter of an inch, with about one inch of overlap for you to fuse.
  • Use an old pen cap or a wallboard anchor to hold your loop while you apply heat and pressure to the weld, or use a short length of clear heat-shrink tubing to contain the weld itself.
  • Using your fingers, press the weld together tightly, allowing it to cool and harden between applications. If you’re using heat-shrink tubing, apply pressure evenly with the iron, especially at the tip of the weld.
  • With the iron, make the weld smooth and tight, and the tip fully bonded.
  • Finally, turn off the iron and, as it cools, tap gently in a circle with the still-warm iron to even out fingerprints and give the line a commercial-grade finish. If you used tubing, cut it away (cosmetically preferable), or leave it in place for additional reinforcement. —Z.M.

Zach Matthews is the host of The Itinerant Angler Podcast,, and a regular contributor to Fly Rod & Reel.