Fly Lines

Fly LinesIf you go back into the history of fly lines, you’ll find that they were made from a variety of materials, but most early lines were made from hair and then silk.  Silk is really the first material that stuck around, and silk fly lines are still being produced today.  But for most fly fishermen today, the more contemporary PVC (or other plastic) fly line is their line of choice.

Up until about 1960, fly lines were given a letter designation to indicate the diameter (thickness) of the line.  But that posed a bit of a problem for the angler, because a fly rod doesn’t load and cast because a line is a certain thickness, it loads and casts because the line is a certain weight.

Obviously, a fatter line of a given material is also likely to be a heavier line, so this letter designation did provide some form of reference for the angler to go by.  But even so, a fly line made of tightly woven silk would be denser and weigh more than one loosely woven, even if they had the same diameters and were made from the same material.

Since the weight of the fly line is what is truly important in loading a rod, another means of designating a line needed to be developed, and in 1959 an organization known as the American Fishing Tackle Manufacturers Association (AFTMA) succeeded in developing and adopting the standard line weight ratings that we still use today.

I honestly don’t know whatever became of the AFTMA, and in many cases people still refer to the standardized line weights as AFTMA ratings.  But the actual standards, including those for standard fly lines, spey lines, and reel feet, are now designated and “administered” by the American Fly Fishing Trade Association (AFFTA).  Of course, my focus in this post is on the standard fly line weight ratings, and those standards range from a One Weight fly line (the lightest) to a Fifteen Weight fly line (the heaviest).

To my knowledge, all plastic fly lines being manufactured today are given a weight rating based upon the weight of the first thirty feet of line, and the line’s diameter is no longer considered.

Silk lines however are still being produced today, and many still utilize the old letter designations to describe them.  These manufacturers use the old letter designations, if for no other reason, than to cover the irregularities in weight that will occur with a product that is being woven from a number of organic threads. But the letter designations will still (in most cases) get you close, if not right on the weight rating you are after.  Of course you will have to correctly convert them, and to help you do that, I’ve included two handy reference tables in this post.

In the first table below, you will find the AFFTA line weight ratings and the approximate corresponding silk line diameter designations.  But like the anglers of old, you need to recognize that these are only approximations, and there will likely be variations in weight from one silk line to another, even if they have the same diameters.  So if you really need to know what the line’s rating is, you’ll have to weigh the first thirty feet of it, and use the second table below.  Most silk line manufacturers or dealers will weigh the lines for you as well, and they can usually provide you with a fly line that falls within your specified AFFTA rating, saving you the hassle.


The next table provides the actual AFFTA line weight standards at the time of this writing.  It should be noted however, that there are also the “ought” weights (lightest to heaviest being: 000, 00, and 0) that are lighter than a 1 weight.  But they are not standardized line weights, and have little support beyond their developer (Sage).


In both tables above I have listed all of the standardized line weight ratings currently designated by the AFFTA for standard fly lines.  As a dry fly fisherman, about half of these line weights are irrelevant to me, because the flies I use never get big enough to warrant their use.  I have included them here however, to provide a complete reference source.

Now in each of the AFFTA line weight ratings, today’s fly fishermen have a variety of options available to them.  So in choosing a fly line (aside from the weight rating and material) you’ll have to consider the various levels of density, the taper types, and sometimes even a choice of colors.  But since we’re only concerned with dry fly fishing, we can also eliminate a number of options categorically, and just get down to what we really need to consider.

Fly lines come in a variety of densities, which is just a concise way of indicating how well they will float (or sink), and so each line is designated as one of four different density types:  a Floating line (F); an Intermediate sinking line (I); a full Sink line (S); or a Floating/Sink line (F/S).  The F/S line is a combination line where the head, or front of the line sinks, but the rest of the line is designed to float.  Additionally (and just as a matter of reference here) all sinking lines will provide a Type (or sink rate) indicating the rate at which they will sink.  For example: a Type III (or Type 3) will sink at a rate of ± 3 inches per second, and a Type VI (or Type 6) will sink at a rate of ± 6 inches per second.

Dry fly fishing however, means surface fishing.  So if the whole line doesn’t float, I don’t want it, and neither will you.  This fact alone eliminates every density type except the designated “Floating” lines, with one other notable exception: silk fly lines.

True silk lines and their “artificial silk” counterparts (typically braided nylon) are technically considered Intermediate (I) sink lines because they will slowly sink if left untreated.  But they are also suitable (and some will claim superior) as a Floating fly line, because these lines, when dressed and cared for properly, will float as well (or better) than a modern plastic Floating line.  So for dry fly fishing, you’ll want a silk line or a designated Floating (F) line, and you can disregard all the other densities.

Next we need to consider the various line taper types.  Certainly there are specialty line tapers, including those that may have been developed specifically for the species of fish you happen to target.  But I’m not going to try and discuss them all here, and will simply state that all of these lines will still fall into one of three line taper types:  a version of a Weight Forward (WF) taper; a version of a Double Taper (DT); or a Level (L) line.

The battles and debates on the pros and cons of each type of taper continue to rage, and they will probably never cease.  But these debates will almost always be between those favoring a DT line and those favoring a WF line, as it is widely accepted by most angler’s that a tapered line casts far better than a line with no taper.  But beyond that, for the moment anyway, let’s just consider what each taper type is, rather than which is “best.”

A Level (or parallel) Line is just that: parallel.  It is the same thickness from one end of the line to the other, with no taper.  Simple enough, so let’s move on.

All Weight Forward (WF) and Double Taper (DT) lines begin with the same three elements: A level tip, a front taper (which could be a compound taper), and a belly (also sometimes referred to as a “body”, but they are the same thing).

A level tip is a short section of line that is in essence a thin parallel line.  This short section of line is the front tip of the line, and is the thinnest part of the fly line.  It is designed to deliver the fly and then land very gently on the water.  At some point though (usually around six to twelve inches from the tip) it will gradually begin to get fatter and fatter until it becomes the thickest part of the line.  This fattening of the line from the level tip to the fattest part of the line is known as the front taper, and the fattest part of the line is known as the belly or body.  So the front end of a WF and a DT taper are basically the same.  They each begin with a level tip, that becomes the front taper, which increases the line’s thickness until it becomes the fattest part of the line, and the fattest part of the line is known as the belly (or body).  But here is where the similarities in the two lines end.

If we cut a DT line exactly in half, and then lay both pieces side by side, each piece will be an identical twin of the other.  In fact, each piece will have the same level tip, front taper, and belly.  So in essence, by cutting the line in half, we cut the belly in half and get two “complete” lines. Since each end is identical to the other, and therefore a double of the other end, the term Double Taper (DT) clearly describes the line’s taper type.

A diagram of a DT line.  Note each tapered end sections are compound tapers, consisting of two different tapers in each section.

A diagram of a DT line. Note each tapered end section is a compound taper, consisting of at least three different tapers in each section. The “belly” of the line in this diagram is referred to as the “body” of the line.

If we cut a WF line in half in the same manner, and lay them side by side, the two pieces will be very different.  The front half of the line will have the level tip, front taper, and at least some (if not all) of the belly just like the DT line.  But the back half of the line will likely be not much more than a long thin level line known as “Running Line”.  Of course to get the line from the belly thickness down to the thin running line, another taper is needed.  So a very short section of tapered line connects the belly of the line to the running line, and this tapered section is known as the “Back Taper”.  The portion of line from the back taper to the front tip of the line is known as the “head”, and depending on the line weight and actual taper design, the running line is usually about one-half of the entire fly line’s length.  So on a WF line, there is a distinct front end of the line (the head) that makes up about half of the line’s length, and a very different and distinct back end of the line making up the other “half” of the line.  As you can see in the diagram below, most of the weight (and thickness) of the line will be in the front (or forward) half of the line.  Hence the term used to describe this taper type: Weight Forward (WF).

A diagram of a WF line, with the back end of the line beginning to the left.  Note that the front taper is also a compound taper as in the diagram above of the DT line.

A diagram of a WF line, with the back end of the line beginning to the left. Note that the front taper is also a compound taper as in the diagram above of the DT line.

As a generalization, WF lines shoot line better, so they are generally preferred for casting longer distances.  They also take up less reel capacity (due to their thin running line) and they are easily the most popular fly line taper type.

DT lines are generally considered to roll cast and mend better (at longer distances where the running line becomes a liability), and some will claim they offer a gentler presentation. Their ability to be reversed when one end of the line wears out is also seen by some as providing “two lines for the price of one”.

My own personal perception on the DT line is they were a real advantage in the days of silk lines, as an angler could “reverse” the line during the day’s fishing when one end became water logged and would no longer float.  So if you fish with a silk line, a DT is still a real advantage, but with modern plastic lines, perhaps not as much.  This reverse-ability does make DT lines potentially more economical in the long run though (or for making two “short lines” by cutting one DT line in half).

These days fewer lines are being made available as a DT, so they are becoming increasingly more difficult to find than a WF, especially since “long belly” WF lines have been developed and provide the extra belly length needed for carrying more line in the air, improved roll casting, and mending.  Irregardless of the taper type though, most fly lines are still ± 90 feet in overall length.

In actual practice, you can probably just take your pick as to which taper type you want to use, as there really isn’t a marked difference in them until you reach the running line.  They both have things they may do a little better than the other given the right circumstances, but nothing you can’t deal with one way or another.  So the lines that are readily available to you, or what you happen to find a great deal on, may take precedence over the taper type in choosing your line.  As a dry fly fisherman though, you can rest assured that a comparable quality DT or WF line will really not handicap you in your fishing.  Your casting abilities will simply be a much greater “limiting factor” than any impact either of these taper types might have on you.  I would stay away from the Level (L) lines though, unless you have a specific reason to do otherwise.  (And if you have a specific reason, you certainly don’t need anyone telling you otherwise.)

I personally prefer DT lines for a number reasons, only a few of which are probably valid.  For example: while I know that a DT line really doesn’t land any more gently than a WF line, I was taught that mentality in my youth (when there may have been a difference), and it still remains with me today.  So psychologically it still matters to me, even if “physically” it isn’t likely to be true.  And any advantage there may be in presentation (real or perceived) I’m all for, because when it comes to dry fly fishing, I don’t think there is such a thing as a line that presents too gently.

Speaking of which… modern (plastic) Floating fly lines typically float through the principle of displacement.  In other words, they “move” (displace) enough water to support their weight.  Silk lines on the other hand use the surface tension of the water to float, by utilizing a “dressing” on them that repels water.  As a result, silk fly lines float more “on” the surface of the water, and plastic fly lines float more “in” the surface of the water.  Silk fly lines are also denser, so for a given line thickness (diameter) they weigh more.  Or put another way, for a given weight, they are thinner.  For example (see photo below) a 3 weight plastic fly line will be “fatter” than a 3 weight silk fly line, but they’ll both weigh the same amount.  I don’t think it takes a lot of mental prowess to understand that a thinner line that floats “on” the surface is less likely to splash around as much as a fatter line that floats “in” the surface.  Which means it will also provide a more gentle presentation.  But again, in actual practice, your casting abilities will be far more important than whether you elect to use a “thin” silk line or “fat” plastic line.  (There are other advantages and disadvantages to both line materials, but I’ll save that for another post.)

Two Double Taper 3 weight fly lines.  The line on top in the photo is a silk line.  the line on the bottom is modern PVC (plastic) line.  Note the difference in line thickness, even though they share the same line weight rating.

Two lines of different materials. They are both Double Taper 3 weight fly lines. The line on top in the photo is a silk line, and the line on the bottom is a modern PVC (plastic) line. Note the difference in line thickness, even though they share the same line weight rating.

In closing, I’d like to provide one last tidbit of information to assist those beginning fly fishermen trying to make sense of all the labels out there.  Here are a couple typical examples of what one might find on a fly line box (also see the photo at the top of this post):

DT4F   or    WF5I

To decipher these, first look for the number.  There will only be one, and it should correspond with the AFFTA standardized line weight rating of the line’s weight.  From there it is generally a pretty easy task to identify the line taper type (DT, L, or WF) and then all that is left is the line density (F, I, S, or F/S)  They may be arranged in a different order (e.g., F3DT) but again it’s easy enough to see the AFFTA weight rating, and then determine which letters apply to the taper type and which one(s) apply to the line’s density.

And just so there is no question here… In the two examples shown above:

  • The one on the left would be a Double Taper 4 Weight Floating fly line.
  • The one on the right would be: a Weight Forward 5 Weight Intermediate fly line.

~ DFG.


4 thoughts on “Fly Lines

  1. mclabrook
    September 12, 2013 at 10:15 pm

    This is a great summary on lines, thanks for writing it up.

  2. Trouter3
    September 14, 2013 at 6:18 pm

    Excellent summation many thanks for the time and effort …it will be a useful piece of information for both
    Veteran and novice fly fishermen ……


  3. Trouter3
    September 14, 2013 at 6:28 pm

    Speaking of lines, just acquired a Rio Lt. DT in -0- weight, why you may ask? I give up, probably cause my curiosity is aroused with much talk and reading about these small diameter fly lines .. I’m going to spool the line on a spare pool I have for Ross Colorado -0- sweet ultra light fly reel … Don’t have a fly rod rated for the -0- weight but the TFO 1/2 weight or the TFO finesse 1 weight will have to do for the test …they both handle the 1 weights very well …..we shall see …. This is like that game, fact or fiction ….


  4. JohnMD1022
    May 11, 2014 at 9:44 pm

    In the late 60s and early 70s a #1 (IEI) or #2 (IFI) Corona or Kingfisher silk line was a hot rig for Pennsylvania limestone Trico fishing. The .022 tip diameter matched well with a leader butt of 0.19, and when tapered out to 14-16 total feet with a 7X tippet, we were ready to go.

    I used to mike everything in those days, using an Ames dial micrometer. Both Ames and Starrett dial gauges can be found on ebay, but there are digital gauges available for far less money. The results of miking can be interesting. I worked for a while at a company which had a breaking strain gauge. Miking and breaking tippet material on my lunch hour was quite revealing.

    In plastic lines, I stuck with the original Cortland Peach 444 as they miked .032 for me, while the SA lines I measured miked out at .037.

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