This might also be of interest;

All dry material like feather, fur, synthetics etc, floats when it is dry.
It is keeping it dry which is the problem.

There are no chemical treatments which will give a fly positive buoyancy.
Most chemical "floatants" are not floatants at all, but waterproofing
agents.

Some of the newer treatment chemicals are hydrophobic. Material treated with
them actually stays dry, and therefore floats.

Some "floatants", rely on the material being soaked with a hydrophobic
material, or at least a material which is immiscible with water. ( Gink,
Paraffin, silicone grease, wax dissolved in various solvents).

Others are hydrophobic in their dry state, ( Watershed etc). The material
thus does not soak up water. The principle is the same, but the dry
materials don´t wash off as easily as the liquid ones.

The specific gravity of the material in use is not the main problem, the
main problem is surface tension.

Cohesive forces between liquid molecules are what cause the phenomenon known
as surface tension. Surface molecules do not have other molecules on all
sides of them, and consequently they cohere ( cohesion = "sticking
together"), more strongly to those with direct contact to them on the
surface. This effect forms a surface "film" which makes it more difficult to
move an object through the surface than to move it when it is completely
submerged.

Surface tension is typically measured in dynes/cm, the force in dynes
required to break a film of length 1 cm. Equivalently, it can be stated as
surface energy in ergs per square centimeter. Water at 20°C has a surface
tension of 72.8 dynes/cm compared to 22.3 for ethyl alcohol and 465 for
mercury.

If you wish to hold a fly ( or anything else) "in" , ( as opposed to "on")
the film, then it must have at two entirely separate properties. It requires
positive buoyancy to keep one end floating, and it must also sink at the
other end.

This is further complicated by surface tension. Surface tension in water is
caused as a result of hydrogen bonding. As stated above, water molecules at
the surface of water are surrounded partially by air and partially by water.
These surface molecules are more stable when they are completely surrounded
by liquid, as all their hydrogen bonds are then fullfilled (cohesion). This
is why water tends to have the smallest surface possible, i.e. it has a high
surface tension, in order to maintain the lowest energetic state.

If a solid material, more dense than water is placed on the surface of
water, then what happens, depends on the nature of that material. If the
material is hydrophilic ("water loving") water is attracted to its surface.
This adhesion of water, to the material´s surface, reduces the surface
tension, and causes the object to sink.

If the solid object is hydrophobic ("water fearing"), then water is unable
to coat the surface. Two distinct forces now come into play -- the energy
required to overcome this repulsion, and gravity. If the force of gravity is
strong enough, it will prevail and the object will sink (assuming that the
object has a density greater than water). If gravitational force is less
than the surface tension. then the object will float on the surface of the
water.

Surface tension is what allows insects to walk across the surface, and
enables a needle to float. The critical feature, is is the amount of force
per unit area. If you put a needle into water end-on , instead of sideways,
then the needle will immediately sink.

Adding detergents and other things to water changes these properties
radically. One hundred years ago, it was much easier to float a fly, as
there were many streams which contained no detergents, road run-off., etc
etc.

Displacement is another problem. A material which is less dense than water
( Cork, wood etc etc) displaces it´s weight in water, but continues to
float.
A material which is denser than water, once it has penetrated the film,
displaces its volume! in water, not its weight!

For instance, say you have a concrete bucket anchor in your boat. You throw
the anchor over the side, what happens? The boat rises in the water, as it
is now carrying less weight. The water in the lake ( although of course you
wont notice this ) actually goes down, because the concrete is more dense
than water, and is now displacing its volume, and not its weight.

Hydrophobic polymers which are less dense than water will float because they
stay dry. More importantly, even after being submerged, they will still
float again when placed on the surface film.

Other materials, ( hydrophilic) will not float again after being submerged,
as they are then coated with water, and so overcome surface tension.
Floatants of course are designed to prevent this. They only work properly on
dry materials of course.

There are not many hydrophobic materials available to the fly-dresser. But
there is a range of positively buoyant materials. Cork, expanded
polystyrene, various foams, etc.

In order to float a fly well, a synthetic yarn must be less dense than
water, and also hydrophobic.

Many synthetics are less dense than water when dry, but will actually soak
up water. These are useless on dry flies, unless treated with floatant.

If you want to tie flies using these materials, then test them yourself in
the bath etc. If they float up to the surface after being submerged, they
are less dense than water, and also hydrophobic. ( Although some may soak up
water over time). This is an excellent device for floating emergers etc "IN"
the film. The fly displaces water, but will still not sink, and it has the
advantage of being a more natural presentation.

For flies that you wish to sit "ON" the surface film, it does not really
matter what you use, although the same synthetics will stay dry
indefinitely, even without floatant.

If you use flies like Klinkhammers etc, then you can get them to "float" at
very precise depths in the film. To whit, the body below the film, and the
"post" in the film, by using the right fibres.

Although the density of many fibres is only a little below that of water,
one may still use the positive buoyancy. BUT the fibres MUST! be hydrophobic
as well.

TL
MC