The Poly Dun

Lightweight and durable, this simple imitation will match almost any mayfly hatch you encounter.

[by Ken Iwamasa]

THERE IS A NEW SERIES OF MAYFLY DUNS for anglers seeking the challenges of casting to rising trout during a mayfly hatch. Poly Duns feature high-profile wings and clean body lines that trigger strikes from even the most wary trout living in calm, glassy waters. And for fly tiers, Poly Duns require few new techniques to the conventional methods used for crafting traditional dry flies.


Polyester yarn comes in many colors and is easy to use. It is perfect for making the wings on the author’s Poly Dun

Float Well and Hold Their Shape

Poly Duns float well because the wings are made of polyester yarn, which is available in many colors similar to the dubbings, Microfibbet tails, and wing materials used for making spinner patterns. These flies have a specific gravity lighter than water, which makes them buoyant. Poly Duns are also very durable.

Separate and blend the fibers of various colors of polyester yarn to create wings of different tones. For example, combine black and white fibers to achieve gray tones or mimic the veins in spinner wings.

Poly Duns feature permanently splayed tails. Simply splay the tail fibers when tying, and apply a discrete touch of superglue to the base of the tail and thread wraps at the hook bend. Apply superglue with a needlepoint tool, such as your bodkin, and use only  a very small amount of adhesive.

Microfibbets are fine synthetic fibers ideal for making the tails on delicate mayfly imitations. A common substitute in a product called Mayfly Tails.

Microfibbets are fine synthetic fibers ideal for making the tails on delicate mayfly imitations. A common substitute in a product called Mayfly Tails.

When tying the wings, strap the yarn across the hook and wrap the thread to hold the fibers in an upright, vertical position. A tiny drop of superglue on the thread wraps and base of the wing fibers locks the post in place. The wing will stand upright and can be trimmed taller than on most other mayfly patterns.


Hook: 2X-fine dry-fly hook, size 16.
Thread: Light tan 14/0.
Wing post: Medium gray polyester yarn.
Tail: Five strands of brown and five strands of yellow Microfibbets.
Body: Yellow synthetic dubbing such as Superfine Dubbing.
Rib: A single strand of yellow embroidery thread.

Tying the PMD Poly Dun

Position the Poly Dun wing post closer to the hook eye than when tying a more traditional hackled fly. Make two complete wraps of hackle behind the wing post on a size 16 or smaller Poly Dun; a larger pattern requires three turns of hackle. Tie off the excess hackle right behind the wing. Trim the wing about 20 percent higher than the length of the hackle fibers.

The PMD Poly Dun shown in the tying photos is an adaptable pattern. Simply change sizes and material colors to match almost every mayfly hatch you encounter.

Ken Iwamasa is a brilliant fly designer who lives in Colorado. If you want to learn more about his terrific patterns, seek out a copy of his book, Iwamasa Flies.