A FLY LINE seems like a pretty simple product—little more than some plastic material gooped around a thin piece of string. The whole thing can be made to float or sink by adding microballoons or heavy metal dust in the coating. However, this apparent simplicity can lull us into overlooking just how much we ask a fly line to do. It has to help us cast by remaining slick; it must withstand the rigors of constant casting, being dragged over rocks, and being stepped on; and it must help us keep our flies in the strike zone, whether it's on the surface or 10 feet down.

As line prices have increased and anglers are deluged with new marketing terminology, it's time to ask, What does it all mean? Is there a way to build a better fly line? And why does my damn tip keep sinking? The answers are not so straightforward as you may think, and there's a fair amount of subjectivity involved. But to get you started, here's your guide to fly-line technology.

Cores and Coatings

"Let's start at the beginning," says Nate Dablock of Cortland Line Company. "Today, most fly lines are made of PVC plastic—the same stuff in plumbing pipes—baked or 'cured' around a nylon core." According to Bruce Richards, the chief line designer for 3M/Scientific Anglers, "Although they are incredibly difficult to make, basically, we make a fly line a lot like you'd make a candle."

THE JET OUTBOARD gurgled to a halt as I stepped out onto a vast gravelly shoal. The river that greeted me was daunting—featuring a yards-wide channel, variable flows, and trout that often seemed just out of range. It's a scenario faced by big-river anglers across the country, and many a rotator cuff has suffered from the stress of repeated monster casts and long-distance mends. But these anglers are increasingly turning to a technical solution—a two-handed rod.