Taper design and line weight are the primary aspects of fly lines but the coatings and cores make up the other essential elements
The core of the line is responsible for the strength of the line, (it “best” not break before your leader does). This means it must be light enough to float and to cast while still having significant tensile strength, (e.g. 1 wt). Next the core is what gives the line its stiffness and its stretch. Too stiff in cold weather, the line forms coils and will not want to pass through the guides. Too soft in the warm tropical water and the line will not form a good loop, (like casting a noodle). The stretch a line has correlates to how much memory it will have and therefore the tendency to coil.
The coating is responsible for mass to density ratio and getting the correct line weight.. Density determines how high the line floats or how fast it sinks. A floating line must be lighter than water. This often involves making the line larger without adding weight. However, the larger the line the more wind resistance when casting. The new hydrophobic coatings actually repel water from lines – this has helped with the problem of smaller diameter lines that maintain their floating capabilities.
To get a line to sink lead or tungsten powder is added to the coating. Tungsten is more expensive but is friendlier to our ecosystems. The diameter of the line is intentionally kept small so the line will sink better, which adds to their castability by decreasing wind resistance.
The pigment that is used in the coatings determines visibility. Both the caster and the fish can see a bright line easier.
The important part of this tip is - buy a line with the taper you need, the core you need and the coating you need, in the correct line weight for the rod you are casting. Then put on the best leader for the fishing conditions and go fish! Easy?
Casting instruction should start again in March
See you there!