Sinking fly lines are must-haves for reaching fish that lurk in the depths. As touched upon in our Fly Fishing Basics - Fly lines & Backing section, there's different types of sinking fly lines out there. With such a wide variety of configurations on the market these days, anglers can really get dialed-in for the specific types of fishing they do. When shopping for sinking lines, you may notice some are labeled with the term "density compensated" or in Scientific Anglers' case "Uniform Sink." This isn't just some unimportant marketing jargon that line companies throw out there; it has noticeable performance benefits!
So what does this mean, anyway? A sinking line that is not density compensated likely has about the same density throughout and will sag as it sinks underwater. This happens because the thin portion of the fly line's taper (near the tip) doesn't sink as fast as the main body portion. Since the main body of line sinks faster than the tip, it causes the line to sag or bow underwater.
A line that's density compensated is made with added density towards the tip so the tip sinks faster which eliminates sag. What are the big benefits? The line sinks in a much straighter path from rod tip to fly giving you a direct connection resulting in better strike detection, easier movement of the fly, and much more efficient hook sets!