Technical · Gear

Above the Film The ultimate guide to fly floatant.

Silicone, cul de canard, and silica each hold a fly in the surface film by a different mechanism. Understand the mechanism and you stop guessing. Ignore it and you spend the hatch false casting a sinking fly.

A dry fly does not float because it is light. A size 18 Comparadun weighs almost nothing, and it still sinks the instant its fibers wet out. What holds it up is surface tension: the skin of hydrogen bonds at the top of the water column, roughly 72 millinewtons per meter at trout temperatures, strong enough to suspend an object many times denser than water so long as that object never breaks through. Everything in a bottle of floatant exists to keep the fly sitting on that skin instead of punching through it. There are three ways to do that, and they do not do the same job.

We are going to take this apart at the level of the surface, because that is where floating actually happens. Once you can see what silicone, a preen-gland feather, and a jar of powder are each doing to the water line, the whole cabinet of products stops being a wall of brand names and becomes a set of tools with clear jobs.

Why a Fly Floats

Start with wetting. Whether a surface stays dry or gets soaked comes down to surface energy. Water has high surface tension and wants to bead on anything with lower surface energy than itself. Bare hook wire, saturated dubbing, matted hackle: these have surface chemistry and geometry that let water spread and climb, and once water spreads into a material it displaces the air, adds mass, and pulls the fly under. That is a wetted, or Wenzel, state. The material is soaked.

The opposite is the state we want, and it has a name worth knowing: Cassie-Baxter. On a rough, hairy, well-structured surface, water does not sink into the texture. It sits on top of it, bridging from fiber tip to fiber tip, with pockets of trapped air underneath. The fly rides on a composite of solid and air, and because air is the least wettable thing there is, the effective water repellency goes through the roof. This is the lotus effect, the same physics that keeps a duck dry. A well-tied hackle collar and a tuft of CDC are not floating on chemistry alone. They are floating on trapped air, held in a lattice of fine fibers.

That single idea reorganizes the entire subject. A floatant's real job is not to add buoyancy. It is to protect the Cassie-Baxter state: keep water from wetting the fibers, keep the air pockets intact, and prevent the collapse into a soaked, sinking mess. The three families of floatant defend that air layer in three different ways.

The Silicone Family

The gels and liquids most of us grew up on are built on polydimethylsiloxane, PDMS, a silicone oil. Its virtue is chemical: PDMS has a surface energy around 20 to 21 millinewtons per meter, roughly a third that of water. Coat a fiber in a thin silicone film and you have lowered its surface energy so far below water's that water can no longer wet it. It beads and rolls off. Some premium formulas push further with fluoropolymer additives, whose surface energy drops toward 18, the same family of chemistry that makes cookware nonstick.

Silicone comes to the fly two ways, and the difference matters more than the brand on the bottle. Gels and pastes (the squeeze-tube standards) are silicone suspended in a thickened carrier. You work a small amount between warm fingers and wipe it onto a dry fly. The film sits mostly on the outside of the dressing. Liquid dips and solvent-carried floatants dissolve silicone in a volatile carrier, an isoparaffin or heptane-type solvent. You dunk the fly, the solvent flashes off in seconds, and it leaves silicone deposited everywhere the liquid reached, including deep inside the dressing where a gel never penetrates. Dips treat more thoroughly. Gels treat faster and give you more control over placement.

Both share one non-negotiable rule: treat the fly dry, before it ever touches the water. Silicone is a water repellent, not a water remover. Put it on a fly that is already wet and you seal the water in, coating a soaked fiber in oil so it can never dry out. Pre-treat a dry fly at the vise or on the drive out, let it set, and it will shed water for a long run of drifts.

Where Silicone Fails

Silicone's weaknesses are all about too much of it, and about temperature. The failure mode nobody talks about is over-application. Load a fly with gel and the silicone floods the gaps between fibers, filling the very air pockets that were doing the floating. You have driven the fly out of the Cassie-Baxter state and into a greasy, matted, wetted one. The fly looks slick and lands like a wet sock. Less is genuinely more. A trace, worked in thin, outperforms a glob every time.

Then there is temperature, because a gel is just a viscous fluid and viscosity tracks the thermometer. In summer heat a paste turns to runny oil that over-applies before you can stop it and weeps into the dressing. In a January tailwater it stiffens to wax you cannot spread thin. The fix is management, not product: keep the tube in a chest pocket against body heat in the cold, and out of direct sun in the heat.

And silicone has one context where it is not merely suboptimal but actively destructive. Cul de canard.

CDC Is Different

Cul de canard is the cluster of feathers around a duck's preen gland. It floats for two reasons at once, and both are structural. First, the barbules are extraordinarily fine and branched, a natural lattice that traps more air per unit volume than almost anything you can tie with. Second, the bird works its own preen oil into those feathers, a light natural wax that adds water repellency without weighing the structure down. CDC is the Cassie-Baxter state in its purest tied form: a cloud of fibers holding a cloud of air.

Now put silicone gel on it. The oil floods that fine lattice, mats the barbules into clumped strands, and collapses the air pockets you were relying on. A gelled CDC fly does not float better. It floats worse, permanently, and no amount of drying brings the loft back. The very product that saves a hackle dry ruins a CDC one. This is the single most common expensive mistake in a dry-fly box.

CDC gets treated one of two ways. Dry powders (discussed next) are the safest choice, because they coat and dry without matting. Or you use a CDC-specific liquid, a thin treatment formulated to deposit repellent on the fibers without the heavy oil load of a standard gel. The rule to carry into the field is blunt: no paste on CDC, ever. Powder or a CDC-rated liquid, nothing else.

Desiccants and the Rescue

The third family solves a different problem. Silicone keeps a dry fly dry. It does nothing for a fly that is already soaked, slimed from a fish, or waterlogged from a dozen drifts. That is the desiccant's job.

Desiccants are fine powders, almost always amorphous silica, sometimes precipitated and sometimes fumed. Silica is intensely hygroscopic: it pulls water out of a wet dressing by adsorption, wicking moisture off the fibers and into the powder. Shake a drowned fly in a canister of the stuff, or dust it with a brush, and it comes out visibly dried and re-lofted. That alone would earn its place in the vest. But the better powders do more than dry. The silica is surface-treated with a silane, typically a dimethyldichlorosilane chemistry, which caps the particles and makes the powder itself hydrophobic. So it dries the fly and simultaneously coats every fiber in a microscopic layer of water-repellent particles, rebuilding the rough, air-trapping texture that keeps the fly in the film. Dry and repel, in one shake.

There is also the fish-slime problem, which desiccants address better than anything else. Fish slime is a surfactant. It lowers the surface tension of the water immediately around the fly and defeats hydrophobic chemistry directly, which is why a fly that floated all morning suddenly sinks after a good trout. You cannot gel your way out of surfactant contamination. You have to remove it: rinse and false cast the slime out, then dry and re-treat. A desiccant does both jobs in one step, which is why a slimed fly wants powder, not more paste.

Two application styles exist. Shake canisters combine silica powder with a residual silicone or resin, drop the fly in, shake, and the fly comes out dried and coated in one motion. Brush-applied powders use a dust-on applicator for more targeted coverage and are gentler on the finest CDC and para-post materials. Either way, the powder is your rescue tool, not your primary pre-treatment. It brings a dead fly back to life on the water.

What We Carry, and When

We stock the bench below because it covers the three jobs cleanly, not because a rep talked us into a wall of bottles. Every product here is one of four things: a gel or paste for pre-treating, a liquid or spray for deep pre-treating, a desiccant for rescue, or a Dry Shake hybrid that bridges the two. Sort them that way and the choice on the water gets simple.

Gels and pastes: your pre-treatment for hackle and synthetics. Loon Aquel is our default squeeze tube. It holds its consistency across a wider temperature band than most gels, so it stays workable when a straight paste would run in July heat or seize in a January tailwater. High N Dry Gel Floatant is a clean, thin-applying silicone gel in the same role. High N Dry Paste Floatant runs thicker and waxier, with more staying power for bushy attractors, hoppers, and big foam bugs. It wants warm fingers to spread thin. All three are for dry flies only, and none of them belong on CDC.

Liquids and sprays: deep pre-treatment that penetrates the whole dressing. Fly-Agra is the heavyweight here. It is a solvent-carried silicone: dunk the fly, the carrier flashes off in seconds, and silicone is left deposited through the entire dressing, not just on the surface. It lasts through long floats and lets you treat a dozen flies at the truck before you ever rig up. High N Dry Liquid Floatant works on the same dip-and-flash principle. High N Dry Liquid Spray Floatant delivers that liquid as a spray, for fast application without a dip bottle. Like the gels, these standard silicone dips are not for cul de canard.

Desiccants: your rescue tools, and the safe choice for CDC. Frog's Fanny Double Duty is the standard we measure the rest against: an ultra-fine hydrophobic silica with the applicator brush built into the cap. It dries a slimed or waterlogged fly and re-lofts it in seconds, and it is gentle enough for CDC and the most delicate para-posts. High N Dry Powdered Floatant with Applicator Brush is the same brush-applied silica approach with targeted coverage. High N Dry Floatant & Desiccant is a shake-bottle combo: drop the fly in, shake, and it comes out dried and coated in one motion. Shimazaki Dry Shake Fly Dryer & Floatant is the original shake canister of that kind, and it brings a drowned fly back faster than anything short of tying on a new one.

The Dry Shake hybrids: liquid convenience without the matting. Shimazaki Dry Shake Liquid and Shimazaki Dry Shake Spray carry the Dry Shake treatment in a flash-off liquid and an aerosol. The carrier evaporates and leaves a fine, powdery, water-repellent coat rather than a heavy oil film, which makes them a rare pair of liquids you can safely run on CDC as a pre-treatment. The spray is the fastest of the two on stream. If you fish a lot of CDC and want to treat dry rather than dust, these are the bottles to reach for.

The Field Protocol

Chemistry only pays off if the sequence is right. The order of operations is where most anglers lose the plot, treating floatant as one undifferentiated step instead of three tools with three moments.

The working sequence looks like this. Pre-treat every dry fly before it touches water: gel or dip for hackle and synthetics, powder or a CDC-rated liquid for anything with cul de canard. Fish it. When it starts riding low, do not re-gel. False cast the water out, then hit it with desiccant to dry and re-loft. After you land a fish, the fly is slimed and needs the full reset: rinse, false cast, powder. Save the gel for the next fresh, dry fly. Match the tool to the material and to the moment, and a single dry fly will fish clean through a long hatch.

None of this is exotic. It is the difference between a fly that sits proud in the film through fifty drifts and one you are stripping in to redress every third cast while the window closes. The bugs are on the water for a reason and for only so long. Spend that time drifting, not drowning.

Surface tension is doing the work. Everything in your vest is just there to keep the fly from breaking through it.

Feather Craft · Est. 1955