I think every fly tyer learned an important lesson with the advent of the Latex Dental Dam craze of the 80’s. Realistic imitation was “in” and natural latex caddis pupa imitations spilled off the pages of Fly Fisherman magaine and into our fly boxes like maggots fleeing a corpse …

We assumed that the waxy softness of wrapped Latex Dental Dam would make the most wary trout succumb, based on its lifelike look and feel, and suddenly fly shops were selling prepackaged Stonefly nymph latex shapes, Latex insect bodies, Latex hopper bodies complete with legs, and we were about to make wild trout kneel before our collective squishy awesomeness.

… then we opened our fly boxes to restock them the following season, and found all that Latex oxidized into broken bits resembling cooked Chow Mein, and realized we had forgotten one tiny little lesson in Physics.

That Which Stretches does not like Sunlight …

Anytime I am contemplating some form of stretchy synthetic in my flies, I remember the painful lesson of latex, and attempt to engineer the material out of the mix, given how little luck I’ve had with elastics.

I have been tinkering with Czech nymphs and their ilk for a bit, and have been slicing the bags the materials came in to make the thin shell backs used on these competition flies. Plastic bags stretch a little, but are not a true elastic material, and I hoped it would last longer than other materials. As the shellback is typically tightly ribbed with wire or monofilament, these flies are less prone to catastrophy than their Latex kin, where the oxidation of the latex eventually unwinds the entire fly body.

“Scud Back” is a material commonly used as the shellback for many of these Czech style nymphs, and I had an idea that I might be able to find the material in bulk form as there are so few transparent elastics used commercially.

Transparent elastic tape is used in the garment industry extensibly, and is used to seal clothing openings, like necks, wrist and anklets, on a wide variety of sports clothing. The transparent color allows it to be sewn into the lining of the aparture without altering the appearance of the outside of the cloth, and is used on nearly every swimsuit, bra, or strapped garment made.

Called “Mobilon Tape” or “Lastin” it is sold in some form by nearly every sewing store, and not suprisingly, for much less than us fly tiers are used to paying. Scud Back is a 1/8″ wide strip of Lastin, available in both clear and dyed colors. 1/4″, 3/8″, and 1/2″ are common sizes of Lastin for garment use, but it can be purchased in 1/8″ wide also. Typically Lastin is available in 0.12mm and 0.15mm thicknesses, just remember that the thinner the material the less likely it will survive hot sun and repeated seasons in your fly box.

Note this is one of the rare times NOT to lay in a lifetime supply. Rather it would prove smarter to replace the material regularly to ensure longevity on your flies. Consider that bras and swimwear see a similar amount of sun and water, it’s likely your flies will last more than a season, but you’ll need to test this due to the uniqueness of your storage method, and your fishing.

I tend to draw the material tight rather than stretch the material over the fly, which reduces the strain on the material and increases its lifespan. My flies are stored indoors in air conditioned splendor, so they are not fried in an overly warm garage, or similar inhospitable space.

Lastin or Mobilon can be dyed, likely with a synthetic dye or acid version, but I am reluctant to weaken the material uneccessarily with colors, hot water, and the mishaps that can occur with increased oxidation. I will dye some later to learn what works best, but that is a low priority.

I have used permanent markers to color the material, but once dry, the color wipes right off.

Most of my Czech nymphs use the simple transparent shellback, but I am contemplating a Hot Pink or Flo Orange Shad fly for use in the American, tied Czech style, so I might add a packet from Hareline just to be clever …

Scud Back is made by Hareline, and sells for $2-$3 for three feet. Lastin / Mobilon sells at most stores around fifty cents a yard, or about $7-$8 for a ten yard bag. Considering how many flies you can tie with a single 10 yard bag, I think I would opt to buy it one bag at a time, mindful to toss it every couple of seasons to ensure oxidation is minimized.

The smaller 0.12mm thickness is perfect for smaller flies, as it is noticeably more pliable than the 0.15mm standard. Extra pliability comes at a cost, as the thinner material likely has a bit less lifespan before snapping. When applying the material onto the fly simply draw it tight versus stretching it to the attachment point, as this will reduce the strain on the material as it ages/oxidizes.

I recieved both thicknesses from garment sources, so you’ll need to read the advert to determine which they are selling.

Mandala Crafts sells 33 yard spools of 5/32 elastic tape for about $9. This material is advertised as a thermoplastic, but doesn’t mention the Lastin brand. The material is clear compared to the slight opaque of Lastin tape, and the material can be stained with permanent felt pen. While useful, it suggests more than a single type of thermoplastic elastic tape exists, so you’ll need to try a couple to see which you prefer.