fly line slickness

Fly Line Technology | Slickness

Guest contribution by John Van Vleet, Marketing Manager at Scientific Anglers. 

Did you miss Part 1: Fly Line Technology | Texturing? Read it here

You might have heard, or read, about slickness additives in fly lines before. They’ve been around for quite some time. This technology always garners a mention on a fly-line package bullet point. But not all slickness additives are the same, not even close.

With the introduction of Scientific Angler’s AST Plus, the difference between simple overcoats and built-in additives is much greater than ever before. To get a real sense of what a slickness additive is and how it performs, let’s first take a look at one of SA’s original additives and then compare it to our newest innovation.


Nearly 20 years ago, back in 1998, SA introduced an additive to its fly line coating called AST, or Advanced Shooting Technology. This introduction was groundbreaking at the time, because no fly lines on the market contained a dedicated slickness agent that was built directly into the coating of the fly line, all the way through to the core.

With the introduction of AST, we added a powdered solid material to the coating of the fly line by mixing it into the colored PVC goop that we use to coat the cores of the lines. This provided several benefits:

  • Reduced Friction — Fly lines with AST were noticeably slicker than previous fly lines, not only to the touch, but also as they moved through rod guides with each cast.
  • Increased Shooting Distance — An immediate benefit of the reduced friction was an increase in shooting distance. Fly lines moved more freely through rod guides and added distance with each cast, which is why we called it Advanced Shooting Technology.
  • Longer Lifespan — AST was built into the fly line’s coating, from the outer surface through to the core, meaning that as fly lines wore down, there would always be AST present; this is in direct contrast to a simple overcoat, which is favored by many of our competitors and dissolves quickly. Their “out of the box” slickness doesn’t last nearly as long as SA’s because it’s not built into the coating.

AST quickly become the industry leader in slickness technology. Eventually, other fly-line manufacturers would introduce slickness additives of their own, which is why we spent several years perfecting a new version of AST, which we (not-so-creatively) named AST Plus.

advanced shooting technology


Eighteen years after the introduction of the original AST, we managed to improve the formulation of AST. AST Plus was introduced in our Amplitude series of lines in 2016. Before I get into the nitty gritty details, here is a anecdote from one of our final casting tests.

At our facility in Michigan, we have a casting pond out front.  This allows us to string up a rod and cast a line at a moment’s notice. One day late in the development process, our Research and Development Manager, Josh Jenkins, lined up five rods.  They all had five identical line tapers, each one built with a different additive. These were the final five formulations that we were to choose between. Throughout the day, everyone in the office gave each line a cast and, unanimously, we all chose the same formulation. That’s a small glimpse into how impactful AST Plus was to all of us at the SA headquarters.


As for how it differs from the original, the main difference is that AST Plus is a liquid-based additive, rather than solid. That difference alone led to one of the most interesting discoveries we made about AST Plus: it actually moves throughout the coating toward the surface, constantly refreshing the outer surface of the fly line with fresh AST Plus. What does that mean when it comes to making fly lines perform better? Here’s a quick rundown of the benefits:

  • The Slickest Lines on the Market — In our tests, fly lines with AST Plus are 50% slicker than lines with our old AST additive. Nearly 70% slicker than lines from any other competitor. (See Drag Chart illustration)
  • Increased Durability — Throughout our durability testing, lines with AST Plus lasted, on average, 8 times longer than other lines on the market. (See Durability graph)
  • Maintains Slickness — One of the most unique, and beneficial, aspects of AST Plus is that it is a coating additive, meaning it is built down to the core of each line and not just an overcoat that can wear off quickly. As our lines wear, AST Plus moves throughout the coating, constantly moving to the surface to regenerate slickness. This means that lines with AST Plus maintain that out-of-the-box slickness long after you spool one on your reel. (See AST Plus illustration)

What Does This Mean for You?

While facts and figures are fine, anyone can create a statistic that shows their line in a positive light. The true test of a fly line with AST Plus is on the water. We’ve been fishing lines with AST Plus for over two years now and the takeaway is clear. At SA, we have hundreds of years of combined fly-fishing experience and the AST Plus is like nothing we’ve seen before. It’s a true game changer in every sense of the word. From presenting dry flies to sipping brown trout, AST Plus simply makes our lines perform better.