Actually Tom, fluorocarbon and nylon are both polymers, and any line containing fluoro & nylon IS a copolymer line.
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A copolymer line can be a combination of different nylon polymers or a combination of nylon and fluorocarbon.
The word hybrid however is more specific, because it tells us that both nylon & fluorocarbon are present.
In other words, all 'hybrid' lines are copolymer, but not all 'copolymer' lines are hybrid.
My pet peeve is the number of excellent anglers and authors who use the words “Nylon” & “Mono” interchangeably.
What Is Mono Line?
The term "monofilament" is self-explanatory, it refers to any line
comprised of a 'single-filament' (as distinguished from 'braided' line).
The most commonly used monofilament materials are Nylon, Fluorocarbon,
Bioabsorbable Polymer and Copolymer (which is any combination of the first 3 polymers).
There is one caveat however: not all 'copolymer' lines are 'monofilament' lines.
A copolymer line with a separate core and sheath is known as a 'cofilament' line.
Roger