Fly Line Backing

By Chris O’Byrne

Out of sight, close to mind.
Pink layer is 200 yards of 20 pound Dacron backing, insurance in the event of a long run.

Backing serves a few functions beyond letting us know when our fish is getting away. First, it takes up space in the portion of the system where the loops of fly line are very small. If your fly line were tied to the middle of your reel, small and long lasting loops would all but destroy the line. Backing also saves money. Fly line can cost over $1 per foot.

Since fly line backing can cost only pennies per foot, the function of taking up space is cheaper with backing. Most importantly, backing helps you catch fish. In Florida, we grow fish that require long casts and that run when struck with the hook. They will bring your backing to hand and make you glad that you paid attention to it.

Installing backing or changing fly line? Be very careful to avoid a tangle like this.

Modern backing is made from high tech chemicals which are extruded into threads, then braided together multiplying strength and stretch resistance like a fasces. The primary materials used for backing today are Dacron and gel spun polyethylene. Dacron, the trade name for a synthetic polyester, is wider than gel spun, so you will be able to carry fewer yards of it. Gel spun polyethylene is much stronger than Dacron, allowing for a thinner line; thus, we can fit up to 60 percent more gel spun backing on a given reel. Strength and capacity benefits of gel spun are purchased with a much higher price and some undesirable characteristics.

Backing is rated for breaking strength in the same manner as general fishing line. Twenty- and 30-pound test are common and 35-pound backing is available. Heavier backing is used only in rare applications, such as marlin fishing with 14-weight gear. Twenty-pound Dacron is sufficient for most Florida inshore and freshwater fishing. Many specification charts will show that a large arbor saltwater reel will hold hundreds of yards of gel spun backing, but do you need or want this line?

For most saltwater species, Capt. Jon Cave goes with the basic 20-pound Dacron, same as he uses for largemouth bass in the St. Johns River. The distances that a redfish will run will not take out enough backing to merit the extra length of gel spun. Same goes for snook, as Norm Zeigler of Sanibel Island writes in his book, Snook on a Fly.

The extra cost of gel spun is more defensible during the run of a big tarpon or permit. Industry pros suggest using gel spun with 9- or 10-weight rods. Beware: Thin gel spun, ripping out between your index finger and the grip, can cut you.

To attach backing to your reel, the arbor knot or uni knot will work. The first wrap must be snug to the arbor or tangles will cause problems. The thin gel spun wraps may dig under the previous layer if wound on with too much or too little tension. When I spool reels I squeeze the backing between my thumb and index finger, shielded with a handkerchief.

Next decision is connecting backing to fly line. The nail knot holds well when using Dacron. Get the wraps lined up like teeth on a comb, and test the knot by pulling the line and backing with gusto. The thin diameter of gel spun makes attaching it to the plastic outer shell of fly line a little more difficult. If you use a nail knot, check regularly for signs of wear on the fly line. An Albright knot, spliced connection or loop to loop connection will wear less on the fly line.

After fishing in salt water, over a particularly abrasive bottom or even after many trips to dark fresh water, strip the backing off, rinse it clean, and then allow it to dry. Dacron can mildew over time, though Tim Daughton of Orvis assures us that gel spun will not corrode or break down. Inspect Dacron or gel spun for signs of abrasion from sand or salt or loosening braid. Be sure to wind the backing on properly again. An inexpensive line winder makes this easy, or a fly shop might inspect and remount your backing for a nominal fee. FS

First Published Florida Sportsman March 2014