Ask MidCurrent: Does a 100% Knot Really Exist?

A quick YouTube search turns up a bunch of videos about “100%” knots.

Question: I’ve always used an improved clinch knot to tie on flies and a double surgeon’s to attach tippet. My fishing buddy keeps telling me I need to switch to “100% knots.” Is there really such a thing?
—Mark C., via email

Answer: The short answer is No. Fly fishers love nothing more than arguing about the relative merits of knots. Everyone has their favorites, and they ain’t shy about telling you why your knot choices are wrong. You’ll occasionally hear that such-and-such a knot is a “100% knot”—meaning that it’s just as strong as straight, unknotted leader material—but when you think about how knots actually work, you quickly realize how unlikely this is.

Understanding Knot Strength

Every knot, no matter how well-tied, creates stress points where the line bends and compresses against itself. These stress points inevitably weaken the line to some degree. Even the strongest fishing knots typically retain only 80-95% of the line’s original breaking strength.

In practical terms, a true 100% knot would mean that if you have a line rated for 10 pounds of breaking strength, the knot would hold firm until exactly 10 pounds of force is applied—the same point at which the straight, unknotted line would break. This would effectively make the knot “invisible” from a strength perspective, as if the line were one continuous, uninterrupted strand.

Why Knots Fail

To understand why a 100% knot is impossible, we need to look at how knots work at a structural level. When a knot is under load, the force isn’t distributed evenly throughout the connection. Instead, stress concentrates at the sharp bends where the line turns back on itself. These concentrated stress points create weak spots where the line is more likely to fail.

Additionally, just the act of tying a knot damages the line at the microscopic level. Modern leader materials, monofilament or fluorocarbon, are engineered with precisely aligned molecular structures. When we bend and compress these materials to form knots, we disrupt their structural integrity. This disruption is unavoidable and contributes to the reduced breaking strength of knotted lines.

Monofilament vs. Fluorocarbon

Whether you use monofilament and fluorocarbon material significantly impacts knot performance, as they behave quite differently when tied into knots due to their distinct molecular structures and physical properties.

Monofilament is more supple, with greater elasticity, so it tends to be more forgiving when tied into knots. It maintains better knot strength across a wider range of knot types because it can deform slightly under pressure without breaking. This characteristic makes mono particularly good for knots that require multiple turns or coils, such as the improved clinch or surgeon’s knot. The material’s flexibility also means that knots can be cinched down more smoothly, reducing the chance of friction-induced damage during tightening.

Fluorocarbon, by contrast, is stiffer and less forgiving. Its harder surface and reduced elasticity mean that your knots must be tied with greater precision and care. Fluorocarbon has a tendency to “bite” into itself when knots are cinched down without proper lubrication, which can create weak points. However, when tied correctly, certain knots like the Palomar or Double Uni can actually achieve higher breaking strengths in fluorocarbon than in mono.

Temperature also affects these materials differently. Monofilament knots tend to weaken more in warm conditions, while fluorocarbon maintains more consistent knot strength across temperature ranges. This becomes particularly relevant when you’re fishing in varying weather conditions or at different depths.

Static Load vs. Impact Resistance

When discussing knot strength, we also must distinguish between two critical types of force: straight-pull (static) strength and shock (dynamic) strength. This distinction is often overlooked, but it can be the difference between landing a fish and losing it.

Straight-pull strength refers to how much steady pressure a knot can withstand before failing. This is what’s typically measured in laboratory tests and quoted in knot-strength ratings. When a knot is tested this way, force increases gradually until the breaking point. These conditions rarely mirror real-world fishing situations, where sudden impacts and directional changes are common.

Shock strength, by contrast, measures a knot’s ability to absorb and withstand sudden impacts, like when a fish makes an unexpected run or surge. A knot might test at 90% breaking strength under steady pressure but fail at much lower weights when subjected to sudden shock. This phenomenon explains why anglers sometimes lose fish to broken knots even when fishing well within their line’s rated breaking strength.

Different knot designs handle these forces differently. Some knots, like the Uni Knot, maintain relatively consistent performance under both static and shock loads. Others, such as the blood knot, may show excellent straight-pull numbers but perform poorly under impact. This disparity is particularly pronounced in fluorocarbon leaders, where the material’s inherent stiffness can make knots more vulnerable to shock failure.

The relationship between static and shock strength also varies with line diameter. Thinner tippets typically show a greater disparity between their static and shock strength ratings. This is one reason why experienced anglers often opt for slightly heavier tippet than theoretical calculations might suggest – they’re accounting not just for straight-pull knot strength, but for the additional vulnerability to shock loads.

What Does It All Mean?

Once you realize that the 100% knot is a myth, you’re still left with the question Which knot should I use? The answer is unscientific, but undeniably true: You should use the knot that you can tie perfectly every time. A knot that’s rated 90% but is poorly tied will almost certainly break before a well tied 80% knot. Practice, attention to detail, and proper lubrication during cinching are ultimately more important than laboratory-measured breaking strength.