The DT versus WF myth (and why fly line companies hates DTs)

The numbers of fly lines available these days are astounding. If you look carefully the majority of fly lines on the market are variations on the (Weight Forward) WF form factor.

The main reason the WF form factor being predominate, one has to look from the manufacturers point of view. Fly line companies are developing many different variations on the WF form factor. More variation on the WF theme is more sales!

The name weight forward is misleading too. A WF is basically a DT chopped in half and integrated with a thin coated running line. There is no weight put forward than there is on a DT (unless it is designed to be as such, see the section about fly line design).


Let's start with the origins
The Double Taper (DT) line as profile (or form factor) comes from the days we used silk fly lines as our every day lines. The reason the DT form factor was developed was to prolong the day's fishing. Once one part of the fly line got water logged and didn't float well (despite being greased) you turned over the fly line and you got to fish the dry part for another couple of hours. Pretty smart!

Cortland invented the modern PVC fly line in 1953. The modern fly lines with a plastic (PVC or Polyurethane) coating eliminates the problem of the old silk fly lines getting water logged as the outer coating protects the inner braided core from getting wet.


Fly line, the 'money maker'
Until around 2000 fly lines were just a 'necessity'. Check out the line section in the Orvis 1984 catalog. Just two floating line models, one economy line and a high end line in a DT and WF. The niche lines here was a line with a fluorescent coating for fishing in low light situations and a shooting head. That's it!

Things started to change some 20 years ago. Fly line companies, especially Rio which was acquired by Far Bank Enterprises (investment company that also owns Sage and Redington) in 2005 from the original founder Jim Vincent, started to experiment with different fly line designs for both single hand and double hand rods to try to help fly fishermen use the right fly line for the type of application or condition. So nowadays fly line companies like Rio, Scientific Anglers and Airflo have specialized fly lines for virtually every situation (wind, delicate, distance, dry fly, nymph, streamer, etc.) and every type of fishing (trout, bass, redfish, bonefish, etc.) imaginable.

Now from a business standpoint this development is pure genius as fly line companies get to sell a lot more fly lines than they used to! Fly line companies are developing many different variations on the WF form factor as the DT form factor has less possibilities to make variations as well as being more costly to manufacture.

One of the biggest changes in recent fly line history is caused by the ever increasing stiffer rods of the last 15 years. Fly line companies started to make lines to get these fast rods load a bit easier. This is done by making them much heavier then they used to be. Lines like Rio's Gold and SA's MPX are about 1.4x to 1.5x line weight heavier. Some lines are even a full line weight heavier! One could question why don't the rod companies just make rods that casts fine with the fly lines within the regular mass specifications by the AFTTA?... 🤔


Now lets talk about a few myths about the DT!

Myth 1: DT presents more delicately than WF

One of the most persistent myth of the DT is the idea that a DT allows a more delicate presentation than a WF.  If you pick up a fly line brand that has both WF and DT versions of the same model (e.g. Cortland 444, check the picture) the profile of both lines are identical up to around the first 30 - 35 ft.

So far there has been only one exception with a fly line model that was available as a DT and WF: the (now out of production) Rio LT from the late 2010's where DT and WF had a deliberately slightly different design.

Unfortunately these days there aren't many companies that sells a fly line both as a WF and DT with the same taper design. 

Update: As per early 2022 Cortland sells two line models both in DT and WF (444 Peach and Sylk) and Orvis (Hydros DT and Hydros WF). Rio sells the Mainstream both in DT and WF but I'm not sure whether they have the same taper design.

Myth 2: WF casts further than DT
The typical WF is in fact not the best choice for distance casting! A WF's belly usually ends around 35 ft. Once you're casting past the belly and into the thin running line, you're 'out of gas' as the thin running line won't turn over the thicker and heavier belly portion of the line very well. Yes, you can shoot the fly line once the belly is out of the rod tip, but the distance gained is a lot less than expected.


So what should I use for distance casting?
For distance casting you try to get maximum loading of the rod to use the energy stored in the rod to 'kick out' the fly line as far as possible. The DT with it's longer belly is actually ideal since the additional mass in the longer belly is what you need to bend (or load) the rod deeper. With your casting stroke you are pulling (the mass of) the fly line (like in tug-of-war) against the tip of the fly rod resulting in loading the rod. As long as the rod can release the stored energy to pull the fly line in the direction of the cast, the fly line will follow.

But trying to achieve distance with a DT, there is a penalty compared to the WF with the thinner running line. The remaining thicker & heavier belly portion of the DT slides out the guides less easier (more friction) and cause more drag (wind resistance) in the air during its flight. You will need a rod with a strong butt section to cope with handling the fly line with all that mass (it's a DT remember?) in the air.

The so called Long Belly fly line (a bit of a crossbreeding between a DT and WF) is what you want for casting controlled long distances. The longer belly (some are up to 60ft) will load the rod deeper similar to what a DT does and on the final delivery cast the thin running line runs through the guides easily. The thin and light running line also doesn't drag during the flight as much as with the DT's thick belly.

Scientific Angler's Expert Distance and Royal Wulff Long Belly are good Long Belly lines. There are variations on the long belly theme. Some lines have a long rear taper that gets smaller in diameter very gradually, almost like a Long Belly. SA's Trout is such a line.

Some recent WF lines are indeed designed as weight forward as in the front belly portion the weight is much more concentrated. These short belly lines have a much shorter belly compared to a regular WF lines. This design allows fast rods to load easier on shorter distances.


So why should we still bother using a DT?
The saying that with a DT you get 'two fly lines for the price of one' is kinda true. As one part gets worn out (coating cracked, stepped on, etc.), you still have the other end you can use that hasn't been exposed to the elements & wear. So far it's true. In real world people turn over the fly line way too late, as in years. After years of storage on the reel the other part is probably all messed up under pressure of layers of line coiled tightly against the smaller arbor of the reel. This part of the fly line will have major memory problems and probably have problems with the tip staying afloat as the tiny air bubbles in the coating that makes the fly line float have been 'squeezed' out.

The solution is to turn over the line regularly, like every 2-3 months. And don't store the line on the reel longer than necessary. Take the fly line off the reel and store it on the plastic container that came with it. This way you will get a longer use of the fly line, like twice as long! And now comes the clue: fly line companies don't like this! They want to sell lines. Once your fly line is worn out they want to sell you another $80+ spanking new WF rather than you turning over your DT and extending the life of your fly line. 😀

So when is a DT 'better'?

+ If you just don't want to buy a new line every (one or two) season.
+ If your rod (and your casting abilities) can handle it, casting longer distances is more accurate.
+ If you make roll casts regularly beyond 30 ft.

+ You can pick up the fly line off the water and immediately cast away rather than first needing to retrieve all the thin running line of a WF line to get into the belly portion before casting.
+ If you mend a long fly line beyond 30 ft (stack mending is the only mending technique at such a distance by the way. See below at one of the updates for more info).

So what are the downsides of a DT?
 Some thoughts to be taken in consideration with a DT:
- You can't have as much backing on your fly reel as with a WF as a DT fills up your reel really fast. Solution: use a larger reel.
- There isn't much choice in DTs these days. Fly line companies usually have only one (if at all!) DT model in their range.
- A DT might not be the best choice for certain conditions (for instance windy) or type of fishing (like fishing with very bulky or heavy flies).
- As mentioned earlier you need to turn over a DT regularly (like every 2-3 months) to take advantage of extending the life of the fly line.

Fly line design

Three major innovations in fly line design

When looking for a fly line for predominantly dry fly fishing, look for a fly line with a long gradual front taper as opposed to one that has a short and abrupt (or blunt) front taper. The first 15-20ft of these 'dry fly' lines are, because of the line design, very 'light' (less mass). Due to its design these type of fly lines don't load a fast rod well when casting short distances. Choose a medium action rod or go one weight up with the fly line if you still want to use a fast rod when fishing close.

Delicate presentation depends on more aspects besides merely fly line design. The most important part being ones casting abilities to make a delicate (applying just the right amount of speed to the fly line on the) delivery cast and some other issues like the leader used (length, leader formula etc.).

Did you know that there are only four fly line manufacturers in the world? That's Scientific Anglers (used to be owned by 3M, now owned by Orvis), Cortland, Rio and Airflo. These four manufacturers produce 95% of the fly lines for different brands like Orvis, Sage (although Sage no longer offers own brand fly lines), Winston, Royal Wulff, Loop, Vision, Guideline, Epic, 406 fly lines, Cabela's, etc. A small amount of fly lines are made in China using less advanced technology. But that could change in the future?...

If you're a rocket scientist and want to get even deeper into the math and physics of fly line, check out this article.

Hope this helps!


Update Dec 10, 2019:
Stack mending is a mending technique that's very effective when nymphing in deep and/or fast moving water where a regular mend won't get the job done. After the delivery cast (overhead or roll cast) is made, cast small roll casts aimed at the tip of the fly line to add lots of slack line. I saw this technique for the first time in the 1980's Doug Swisher's (VHS!) video, "Advanced Strategies for Selective Trout".

Since that video is copy righted, here's a video I found that shows it:



Update July 1, 2019:
I was driving to a business appointment today and decided to listen to a podcast and ended up with one April Vokey did with Carl McNeil, the owner of Swift Fly Fishing. Besides an enjoyable podcast about the history behind the man, Carl also talks about fly lines.

Listen around the 51:00 mark about the benefits of Long Belly fly lines (or even a DT) for distance casting. A more elaborate but very interesting is around the 52:00 mark about how fly rod manufacturers (or designers) rate their fly rod and how arbitrary this is.


Update Sept 3, 2017:
There is one more line manufacturer in the UK: Northern Sport Fishing. This is probably the manufacturer of lines like the Shakespeare Worcestershire lines and Barrio fly lines.
Thanks for the update Thomas!


Update Aug 28, 2017:
Tom from 406 Fly Lines commented on this post.

'Hi Jay,

Very interesting article. I have a couple of comments. 406 Fly Lines does use different profiles between the WF and DT - the reasoning being that we wanted to the lines to have a similar feel from the 2 weight through the 8 weight. Also as a company who deals directly with the Manufacturer I can tell you the cost of manufacturing between a WF and DT is minimal. I believe the real reason companies don't make more DTs is that it's a simple design and the WF can be configured in a multitude of different designs hence more sales. With the rise in popularity of fiberglass rods and the steady sale of cane rods the DT will be around for quite awhile. As an aside our DTs outsell our WFs by at least 4 to 1.'

Thanks Tom for your comment!