This is the 2nd in a series discussing fly lines summarized from Bruce Richard’s MODERN FLY LINES.
Primary Basic Coating
PVC (Polyvinyl Chloride)
Micro balloons/air bubbles-decrease line density, improve floating lines
Powdered tungsten-adjust density for sinking characteristics of sinking-type lines
Different core and coating combinations and their interactions allow for designing specific fly line characteristics. For example, both braided monofilament and multifilament nylon are very limp. However, braided monofilament can become stiff when combined with the coating making it ideal for warm saltwater fishing.
Doc Frangos FFI MCI