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The Flexi Floss Dun

New materials make an old pattern even better

The Flexi Floss Dun

The Flexi Floss Dun (above) uses durable, easy-to-wrap flexible floss for the body (floss shown in the background), Antron yarn for a trailing shuck, and chicken marabou (or CDC) for the wing. It is based on predecessors such as the Haystack, Compara-dun, and Sparkle Dun. David J. Siegfried photo

I was first shown Flexi Floss several years ago at a Federation of Fly Fishers Conclave. Charles Jardine was teaching a class, and I was one of his students. Jardine demonstrated his favorite patterns for stillwater trout fishing in England. He talked about a material called Flexi Floss used in Britain to create Buzzers and other patterns.

Flexi Floss was originally developed by DuPont as a fiber to make fabrics stretch. The original Flexi Floss is available overseas through Veniard dealers. Flexi Floss has been marketed in the U.S. as Lumiflex, Dyna Floss (Cascade Crest Tools), Flex Floss (Spirit River), Spanflex (Wapsi), and several other names. Spanflex comes in different diameters, which makes it useful when you want to tie a wide range of fly sizes.

These products are all interchangeable. Your local fly shop probably doesn’t carry Flexi Floss, but it likely has something similar under a different brand name. I refer to the material generically as flexible floss.

Flexible floss owes its origin largely to the companies that make and sell spinnerbaits for bass fishing. The fly-tying industry soon recognized the benefits of flexible floss and started marketing it as a new leg material.


Flexible floss is resistant to UV light, stretchable, and holds dyed colors. You can color it with a permanent marker or Pantone pen, and the colors won’t fade or bleach from the sun. Because it is synthetic, it won’t rot or break down. It appears segmented when twisted around a hook shank and it is somewhat translucent.


I started using flexible floss as a substitute for natural materials and found it useful for bodies on nymphs, dry flies, emergers, and other patterns. You can substitute it almost anytime you wrap pheasant-tail fibers, stripped peacock herl and hackle quills, or goose or turkey biots.

Because flexible floss is slick and shiny, it gives flies a lifelike sheen. Products like hollow tubing and vinyl ribbing produce similar effects, but because flexible floss stretches to a narrow diameter, the transition points are not as bulky and it’s easier to work with.

Updating the Compara-dun

I wanted to create some realistic patterns for the Delaware River, where the long, flat, clear pools give fish time to look at flies. By updating the Compara-dun, I thought I could take a fly that already fishes well on flat water and improve it by changing the body, tail, and wing material. You can create all kinds of sizes, shapes, and colors with this basic concept. Adirondack fly tier Fran Betters invented the Haystack—upon which Caucci and Nastasi based their Comparadun. The Haystack used deer hair for both the tail and wing. The Compara-dun had a slimmer, more delicate deer-hair wing and hackle fibers for the tail.

Craig Mathews revolutionized Western dry-fly fishing by adding a Zelon shuck to the Compara-dun to create the Sparkle Dun and later the XCaddis. René Harrop, Shane Stalcup, and others later used CDC, biots, vinyl ribbing, and hollow tubing to create their own Compara-dun variations.




By changing the materials yet again, my Flexi Floss Dun design allows tiers to create smaller flies with slim, segmented, translucent bodies. You can also tailor the body color to specific hatches using marking pens.

The chicken marabou or CDC puff wing material lets you adjust the feathers to a variety of fly sizes. This wing type also eliminates issues some tiers have with deer hair, such as locating the right (fine) hair, stacking the hair, and tying the hair wing without creating an unsightly lump in the fly body.

Fishing and Tying

Flexi floss duns fish best in slow, clear water. In fast riffles and pocketwater they tend to sink—this is where the high-floating Haystack is a better choice. If you angle the wing back with dubbing, the Flexi Floss Dun also makes a fine flatwater emerging caddis. There’s no need to change the body design or trailing shuck. Flexible floss comes in a variety of colors to match any mayfly hatch. You can also mix two strands of floss at once to create a barred effect—just stretch the material more when you wrap the doubled strands so each strand is a thinner diameter. Most mayfly dun bodies are light on the bottom and darker on top. To properly imitate this, use white or lightcolored flexible floss for your patterns and color the top with a marker. Add small brown or olive dots along the back for a variegated or mottled effect. You can match any mayfly hatch this way. I suspect you will find—as I have— that flexible floss is a time saver and helps you create more consistent-looking, durable flies.


Mike's Flexi Floss Dun

HOOK: #10-20 Mustad 94840, Daiichi 1170, or similar. 

THREAD: Black 6/0. TAIL:Olive-brown Antron. 

WING: Dark dun chicken marabou (Chickabou) or CDC puffs. 

BODY: Gray, brown, or light olive flexible floss with back marked with a brown marker. 

HEAD: Small dubbed head of muskrat fur or SuperFine dubbing.

1. Tie in the Antron yarn trailing shuck. Taper the ends into a triangle shape. A few uneven strands make it appear even more natural. The longest fibers should be about the length of the hook shank.

  //content.osgnetworks.tv/flyfisherman/content/photos/Flexi-Floss-Dun-1.jpg 

2. Tie in a chicken marabou feather wing with the tip extending over and past the hook eye. Make two or three thread wraps, and then draw the wing butts backward to make the wing length equal the length of the hook shank. Make two or three additional tight wraps, and then cut the wing butt ends at an angle to create a base for a smoothly tapered body.

  //content.osgnetworks.tv/flyfisherman/content/photos/Flexi-Floss-Dun-2.jpg 

3. Move the thread in front of the wing and force it upward by building a thread dam against it. Wrap a smooth underbody with thread. Flexible floss is a thin material and highlights any lumps or imperfections in the underbody. Clean, tight work on the fly base makes your finished fly look better.

  //content.osgnetworks.tv/flyfisherman/content/photos/Flexi-Floss-Dun-3.jpg 

4. Move the thread to the rear of the wing and trap a single strand of flexible floss. Make a single tight wrap. Pull back on the floss to stretch it and wrap back along the hook shank, wrapping the floss down smoothly. Clip the tag end of the floss.

  //content.osgnetworks.tv/flyfisherman/content/photos/Flexi-Floss-Dun-4.jpg 

5. Advance the thread to the flexible floss tie-in point and overwrap the tag end. Make a half hitch with your thread to secure it. Wrap the floss forward in tight, even turns, stretching the material slightly as you move forward. If you introduce slack to the floss, the body will uncoil like a spring. Stop behind the wing. Wrap your thread over the floss locking it in place, and clip off the excess floss.

  //content.osgnetworks.tv/flyfisherman/content/photos/Flexi-Floss-Dun-5.jpg 

6. Stroke the wing with your thumb and forefinger to stand it straight up. Dub a small cone-shaped head to keep the wing in place, and whip-finish. The head should be slightly thicker than the body of the fly.

  //content.osgnetworks.tv/flyfisherman/content/photos/Flexi-Floss-Dun-6.jpg 

*Mike Hogue is the owner of Badger Creek Fly Tying (eflytyer.com) in the Finger Lakes region of New York State.

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