Guest Blogger: Michael Vorhis, author of ARCHANGEL suspense thriller, OPEN DISTANCE adventure thriller & more to come

Figure 1: Loops

We’ve all acquired fly line or sink tip material that lacks end loops, or have blown through such a loop for one reason or another–either by putting too much pressure on a snag, or having a small-diameter leader cut through the loop material, or any of a number of ways to blow one out. Or we’ve attempted to tune our cast by modifying the taper of a given line by cutting off some of the line on the end, and now we need a new loop. Or we’ve sought to resurrect portions of a worn out line by using lengths of it as floating or sinking tip material, and each section needs loops. Or we’ve bought lines that have loops so small we can barely get the knot of a perfection loop through them. Or we’ve caught the belly of a good line on volcanic rock and damaged it to the point that we’d like to splice or loop-to-loop it back together.The point is that we’ve all had reason to want to add a loop to a line, or to repair a loop, or to otherwise join two line portions together. We could go old-school–nail-knots and bits of heavier mono–and that can be very strong…but once the ease of an integral line-loop is tasted, many of us prefer that cleaner-flex-profile configuration. We could tie perfection loops and coat the knots with goo, but those knots get big and our tip guides stay small. We could buy those after-market add-on loops, but one is never sure how well they’ll hold, and they introduce an anomaly in the line (as far as floating and degree of stiffness go), and they’re not necessarily an installable solution while on the stream. We could use epoxy to make a loop and suffer an overnight wait and a stiff section of line where it’s applied. We could trust superglue, equally stiff, but when it flexes the bond may break. We could follow those convoluted thirteen-step advice videos that would have us applying an open flame to the plastic coating of the line and melting ourselves a loop, subsequently to wonder whether we’d heated it too much or too little and how much it will really now hold.

Figure 2: Resins

And then along come a bunch of surf-board dudes and chemical engineers with their magical UV-cure resins, and a promise that from now on our knots can be smooooooov and can slide through rod guides like jelly. Hooray! It sounds like the answer. You just stick stuff together, for a fully cured bond wherever the sun can shine! …except that…we come to realize that many of those products call themselves “coatings” and take great pains to avoid representing themselves as glue.

Why? There must be a reason. Is it simply that nylon line material just will not adhere to any glue of any kind (that much is true) and that these UV-cure products are all too often applied to monofilament nylon? Is it just because those manufacturers can’t be certain how well their stuff is applied and so they err on the side of caution as far as claiming actual adhesion? Maybe. Or maybe there’s not much adhesion at all–maybe these resins are not really a “quick epoxy cement” like we imagined when first we heard of them.

You’ll find no precise answer anywhere on any bulletin board or forum–I know because I’ve looked exhaustively for several years. One could attempt to corner the manufacturers in hopes of getting an answer, but first you’d wait months seeing a response (they are very aware of the words they purposefully avoid), and second, if you ever did get a response it would be something imprecise, something scribbled out by the marketing department’s administrative assistant, something along the lines of, “We recommend you tie appropriate knots to be sure, then coat them with our product.”

So I got tired of wondering; my bring-to-net numbers were hanging in the balance, after all. I set out to perform a few tests. I’d had the good fortune last year of successfully fighting a powerful fish for over 3 hours on a loop I’d made, but the loop hadn’t been particularly minimalist…so better to control the application of the resin and see exactly what kind of strength might result.

My goals:

1. Determine whether the UV-cure resin is just a coating or whether it’s an actual cement.

2. See how much load it holds for different ways of applying it.

My tests used floating line, size L-11-F. The surface area of this line is much larger than most floating lines a trout angler uses, so it’s probable that my results should be scaled back to smaller loads for smaller-diameter lines (and can be scaled up for really fat spey shooting heads). Also, sinking lines are typically impregnated with tungsten powder, so it may well be that adhesion differs for such lines. My experience with them, however, has me convinced that the conclusions I draw here are sufficiently applicable to sinking line materials too.

My tests used “UV Knot Sense” marketed by Loon Outdoors. There are plenty of other UV-cure resin products, each with its own mix of properties, and some of them do call themselves adhesive or glue…so I elected to test the one common product that seems to conspicuously omit that word from its packaging and online claims.

In all cases I initiated the curing with my UV mini-flashlight, but then took care to give the splice a good ten minutes or more in the bright outdoor sun, then turn it over and give it another ten or more. The product I was testing seemed to feel less oily to the touch after this extra curing, so I assumed that strength was improved with a good long outdoor cure.

I made no tests whatever with fluorocarbon or nylon monofilament leaders. Personally I would never omit the knot, for such materials.

Test 1: End-to-End Fly Line Repair

Figure 3: End-to-End Joint

This test was performed only for completeness’ sake; I know of no one foolish enough to attempt to join fly line segments this way and hope for the mend to hold. The joint was made with a small “dot” of UV-cure resin between linearly aligned butt-ends of the fly line segments, as shown in Figure 3.

For this test I hung a light load from the line and noted the cured resin’s ability to hold. A water bottle proved convenient, as shown in Figure 4. I added water in repeated tries until I got a weight that the splice would not hold.

Figure 4: Testing the Bonds

Result of Test 1: The end-to-end-joined splice held no more than about 0.5 pounds before parting. But considering the ridiculous type of joint, that was actually impressive.







Test 2: Simple Overlap Fly Line Repair

Figure 5: Minimalist Overlap Splice

This test almost (but not quite) begins to approach the realm of doing an actual line repair. I overlapped the two fly line segments about 3/8 inch, and applied a small amount of UV-cure resin along the entire 3/8 inch, but only between the two line segments–like glue. Application was not as precise as I’d have liked, but I cured it well, and then tested. Figure 5 shows this joint.

For this test too I hung a partially filled water bottle from the line and tested for strength, adding water a little at a time until the splice failed.

Result of Test 2: The minimalist overlap splice held remarkably well, considering the “peel” forces on it. It gave way somewhere a little above 2.5 pounds.

Test 3: Overlap Splice, Fully Coated

Figure 6: Fully Coated Overlap Splice

This test begins to make proper use of the surface area available. As with test 2, I overlapped the two fly line segments about 3/8 inch, but this time I applied UV-cure resin entirely around the joint, including the ends of the line segments (which I feel is important because doing so reduces the “peel” forces on the joint). Resin amount and application was consistent with many joints I’ve made in the past, so this test represented what a good repeatable resin application could do. I cured it well and then tested. Figure 6 shows this joint.

Beginning this test, I began to use a digital scale I purchased for weighing luggage and fish; it is accurate to 0.01 pounds (~0.16 ounces). I increased the pressure smoothly to get an accurate reading at failure.

Figure 7: Failure of Test 3

Result of Test 3: The fully coated overlap splice held a solid 9.58 pounds, and when it failed it was not because of the resin bond itself. Instead the braided core parted wit the line’s coating, along a quarter-inch stretch of one line segment. See Figure 7.

Note that the entire load was still pulling/peeling semi-linearly along one bond…and yet it still held quite a bit. This differs substantially from the even better scenario of a loop, as you will see in test 4.

Test 4: Loop, Fully Coated

Figure 8: Loop Made With Resin Only

This phase of the study tests the most practical configuration of the four so far because it evaluates the strength of a loop formed using UV-cure resin. With a loop, only roughly half the load is working to part the splice, and the shear force is much more linear, with no “peel” forces applied. I made a loop by overlapping the tag-end approximately 3/8 inch along the line. As with Test 3, I applied UV-cure resin entirely around the joint formed by the two parallel sections, including the end of the line and where the joint just begins to widen into a loop. I cured it well and then tested. Figure 8 shows this joint.

I attached the 15-pound-test butt of a leader to the loop I’d made, using a loop-to-loop connection, and measured the supportable load using the digital scale.

Result of Test 4: The fully coated loop joint held to over 20 pounds with no sign of damage, and I did not take it all the way to failure, as I didn’t want to break the line. (Even fly line manufacturers don’t usually warrant their loops beyond 20 pounds.)

Figure 9: Loop Damage from 20+ Pounds

And although the loop held, this amount of pressure did permanently damage the line coating, as Figure 9 illustrates.

As the figure shows, the loop of the thick 15-pound-test leader cut right through the fly line coating. And yet the braided core of the line, which bonded to the line coating which was then in turn bonded together by UV-cure resin, still held at 20+ pounds. No thread-wrap, no super-glue, just UV-cure resin “encasing” the joint. This means that this type of loop is quite viable for most fly angling purposes.

Test 5: Loop Made with Thread and Resin

Figure 10: Loop Made with Thread & Resin

This was not really a test; I did not want to damage this piece, as it’s a real part of my actual fishing arsenal. However I provide a photo of this kind of loop in Figure 10.

To make such a loop, it helps to be able to pull tightly when winding the thread. I first join the parallel line areas with a tiny spot of super-glue just so nothing will move on me, then lay a very thin sewing needle along the parallel line portions. I wind the thread as tightly as I can with the help of the stiffness the very thin needle provides. (I have tried using a special thread that shrinks to 60% of its length when it’s subjected to steam, but I’ve come to the conclusion that it doesn’t shrink with any real force and I don’t realize any useful compression from using it…but it seemed like a good idea at the time. So I use any strong thin thread. I do not use monofilament because I want the extra friction a braided thread provides.)

Finally I pull out the needle (not so easy…requires a pair of pliers), coat the entire joint with resin, and cure it well. If you forget and leave the needle in there, no worries because one fine day it will remind you.


I provide a table showing the test results I achieved.

Table of Results

I think there are positives and negatives to using thread to wind a loop joint. Three positives are that it slightly increases the surface area the resin will coat, it adds a small measure of friction that impedes the fly line sliding with respect to itself, and it tends to compress the line coating together nicely as long as you can get it tight enough…which is by no means a given after the needle is removed (which is why an extremely thin needle is recommended). One negative to using thread is that it shields the line coating from bonding with the resin. I think from what I’ve learned in these experiments, in future I will use *some* thread but not enough to keep the resin from touching and bonding well with the fly line…as Figure 11 illustrates. The test results prove that the line-resin bond is worth a lot.

Figure 11: Loop Made with Less Thread

Again, I believe the right thing to do is to scale the results I measured by surface area; of which thinner lines naturally have less. Circumference of a circle is given by the equation “pi times diameter,” which means circumference scales linearly with diameter. So a fly line tip that’s 2mm in diameter will have twice the surface area per linear length of line than does a fly line tip that’s 1mm in diameter. So to achieve with 1mm-diameter line the strength equal to what 2mm-diameter line holds, simply double the length along which the resin is applied.

Finally, I think it’s obvious that this resin stuff is definitely cement–at least for fly line coatings anyway. Promote a good bond (clean surface, good curing, sufficient surface area contact) and you’re on your way to having a line feature that will hold when you need it to…and one you can rebuild right there mid-current if you have to.

So bend a loop, lay that tag end up against the other part of the line, and stick it! …where the sun does shine.


  1. Good article. Practical testing and results. Personally, I don’t like loops. If nothing else, they collect scum and weed. They also alert the fish by causing a disturbance on or under the water. I do use non slip loop knots to attach flies to tippet, as that allows more action. I contend that there is nothing better than the old nail knot, properly executed.

    1. No-Slime, you bring up a great point although I suspect it may be a losing battle convincing the world to stay with old-school…convenience will win in the end I’m afraid. Myself, back before factory loops, I would nail-knot a piece of thick mono to the line’s end and put a loop in that mono. I’d read all the nail knot advice and yet saw all the leaders being sold with loops on them, and amazingly I thought I had invented the loop-to-loop connection! I was young and emarrassed to show it to older anglers because I feared they’d berate me for the “splash” my connectio would inevitably make. But it was just so danged convenient and I reasoned that I’d simply use a slightly longer leader to make up for the splash.

      Algae collection is a great point although smooth factory loops are less guilty than hand-tied…and now that we can coat our leader loop knots with UV-cure goop, we can further reduce the salad we dredge up. I too hate green blobs on my line but where I get the problem most is on blood knots, because I still hand-tie and hand-taper my leaders a lot of the time (I guess that’s my brand of old-school…or maybe I’m just a miser). Again, the resin helps on blood knots if I take the time to use it.

      I guess I suffer the downside of loops because I can switch in a bit of poly-leader, or a leader of different length, while on the stream…and not need different reels…and not need to carry a nail, which I’d surely find a way to poke through my waders if I did carry one.

      But I salute your sticking with the purist approach, and hope to never lose it completely myself. Tnx for championing the old ways.

      – Mike

    2. Hi, No Slime,
      I contend that there is ONE thing better than the old nail knot, properly executed and that’s a nail knot that goes through the core of the line tip.
      For some time now, I’ve connected my leader to the fly line by poking a sewing machine needle a little way into the tip of the line and pushed the point out of the line around 8 to 10 mm from the tip. Then I feed the tip of the leader into the eye of the needle, withdraw the needle from the fly line and then pull the whole leader through the tip of the line until there is just enough leader butt left to tie a nail knot. This effectively makes the leader an extension of the core of the fly line so there is no hard edge to the transition between the leader and line to catch on the guides. It’s a little fussy but if you take care of leaders so you’re not changing them every session, it’s certainly worth the effort. Especially when a large fish takes a run just as you’re about to net it.

  2. What about using a bobbin and tying thread for the thread? Maybe a touch of super glue to hold the tips together, then start your wraps on the line side of the loop, wrap down towards the loop as far as you like and then just make a 5-7 wrap whip finish. Put the resin on, let it soak for a few minutes and then zap it. Then cook it in the noonday sun for a few minutes. Just some thoughts.

    1. Hi Bill, good point about the bobbin, and I’ve tried it. You’re right that it adds a measure of control, but you still cannot bear down on the thread much unless the section you’re wrapping is stiff–hence the thin needle. Use of a needle makes a bobbin a nice additional luxury rather than a requirement. But yes, certainly.

      I ran through what I think was every conceivable method of wrapping thread tightly, including use of an assistant, but the thin needle was by far the most successful element.

      The super-glue does help–to keep the sections aligned until thhe thread and resin can be applied…and probably helps with the load in use too.

      – Mike

  3. Use shrink wrap first over tag/line ends of loop , then coat with thin UV resin 9there is a video on YouTube about this)

    1. Hi Arthur, thanks for the comment. I’ve seen numerous videos using shrink wrap, but it’s very difficult to know just how much pressure some shrunken shrink-wrap (and there are many types) applies…and how much heat to apply, and how long…and how to get max shrinkage and still avoid all damage to the line. You might be right but I found the thread to be more controllable by me, and to let me know afterward how tight it really is, and it soaks in the resin so it becomes an integral part of the bond.

      But it’s true I could be missing something. In my (electronics) profession there are lots of kinds of shrink tubing but heat application is usually less than precise. I guess I don’t trust myself going that route. If you find it’s terrific, by all means post your results.

      – Mike

  4. Hi Mike,
    Nice work. As you might recall, I am a chemist. Your testing procedures should lead to your nomination as an honorary scientist. Good work! In addition, you answered a question I have been unwilling to answer, so thanks for that.
    Finally, I am not a fan of fly line loops at the end of my fly line. They always seem to get caught in the guides when you are trying to pull out your line. In addition, eventually they always wear out (however, you have solved that problem). I have switched to the method of super gluing a segment of 20-30 lb mono into the end of the fly line and making a perfection loop 9-12″ away from the mono-fly line attachment. This allows me to make loop-to-loop connections. Pulling the loop-to-loop connection firmly seats the two loops and gives a much lower profile that barely catches (if at all) in the guides. So far, I have one that has lasted two seasons without failing. If it makes three seasons, that’s about the useful life expectancy of the fly line.

    Thanks again for excellent and pain staking work to answer an important question.
    All the best, Joe

    1. Hi Joe, thanks for weighing your scientific mind in here. Remember I’m an engineer on non-fishing days, so precision, thoroughness and accuracy in root-cause and solution assessments is no stranger to me…although I concede that engineering and science are not the same thing…I think of engineering as “playing science fast and loose.” : )

      The “going through the guides” thing is an annoyance but I just deal with it. Coating the knots helps a bit, as a loop itself is inherently rounded.

      Your approach to leader attachment is kinda like I used to do (see my reply to No-Slime above). But I would never have dreamed that super-glueing a hunk of mono to the line’s end would hold! Do you wrap it with thread? Do you coat it with UV-cure resin? Wow…you’re a brave man. Last October I hooked into a big Chinook on my small-trout rig and it took more than three hours to land (you may recall I told the tale here o0n the blog). I Was terrified that the 3x tippet would pop. Had I also attached leader to line the way you describe, well, let’s see…it’s August now…I think I’d still be out there applying no more than 5 ounces of pressure and hoping to tire the thing out.

      – Mike

  5. Hi guys, thanks for the comments. I am still off-shore (have been for a few weeks, and unfortunately I din’t mean wading a stream), so I’ll respond on my return early next week. I enjoyed glancing through your comments very much but I want to read them more carefully, the better to learn from them and to respond with accuracy.


  6. Incidentally, I had the pleasure of trading some emails with a chemical engineer who develops these UV-core resins. He confirmed a few fascinating points:

    A. Most, if not all, these resins do adhere to porous materials, making them epoxy-like in their bonding ability.

    B. Some UV-cure resins cure when UV light strikes the resin, and some cure when UV light strikes a catalyst mixed into the resin.

    — i. Resins that are themselves sensitive to UV light require the light to be applied to all portions of resin that want to cure…so using them to repair opaque items like coffee cup handles won’t work because the resin not reachable by the light will never cure. Resin clarity is imperative, so that the light will go through all the resin. This kind is best suited to our tying and line-working needs.

    — ii. Resins that have a catalyst in solution can cure as long as any part of them is exposed to UV light–the catalyst starts the curing that, once begun, keeps going even in the resin that doesn’t get directly illuminated. This is called “shadow-curing.” It means that if a bit of UV light momentarily strikes the top of your bottle of tying resin, the next time you reach for the bottle you’ll find it to be a solid lump of fully cured, useless resin. These products are advertised as “repair-all” products and are obviously ill suited to our purposes.

    The gentleman who explained this stuff to me (and I think I describe it essentially right, although I may be a little off on a fine point or two) is a true expert and a J.Stockard blog frequenter. I am very grateful to him for schooling me on the different ways such products work.

    – Mike

  7. You can apply a thin coating of Pliobond Glue to your nail know connection to you butt section to help it slid easily through your guides and it will not collect moss in most cases. Pliobond has been around and doesn’t take that long to setup. You can fix holes in your waders with it also.

  8. On the splice, it possibly would be better to scrape off one side of the coating on each end so that the bond is core to core, cure, then coat the entire joint and cure again. ??

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