What backing does and why you need it
Backing is the thin, strong line wound onto your reel spool before your fly line. It serves one purpose: to give you extra line when a fish runs farther than your fly line can reach. Most fly lines are 80 to 100 feet long. A large saltwater fish or a fast trout in a wide river can strip that distance in seconds. Without backing, you hit the end of your fly line and either break off or lose the fish.
Backing also fills the reel spool. A fly reel works better when the spool is nearly full — the larger diameter means line comes off faster and with less memory (coiling). A mostly empty spool with just fly line creates tight coils that resist casting and mend poorly. Backing solves both problems at once.
The amount of backing you need depends on what you are fishing for and where. A trout stream angler might never use it. A saltwater or steelhead angler will absolutely need it. The difference is the size of fish and the distance they can run.
Key Takeaways
- Backing fills your reel spool to improve casting and line management, and provides extra line when large fish run hard.
- Trout anglers typically spool 50 to 100 yards of backing; saltwater and steelhead anglers need 150 to 300 yards depending on reel size and target species.
- Braided backing is standard because it is thin, strong, and does not absorb water, making it reliable in all conditions.
- Backing must be attached to the reel spool with an arbor knot, and to the fly line with a Bimini twist or nail knot.
- Spooling backing onto a reel is easier with a hand crank or motorized spooler, but can be done by hand with patience.
How much backing to spool
The amount depends on your reel size and what fish you are targeting. A standard trout reel (size 5/6) holds about 100 yards of backing plus an 90-foot fly line. For small streams and ponds, 50 to 75 yards is enough — most trout do not run far. For larger rivers and lakes where trout can make longer runs, 100 to 150 yards gives you a safety margin.
Saltwater reels are larger and need more backing. A 9-weight saltwater reel might hold 200 to 300 yards. Steelhead and salmon reels typically hold 150 to 250 yards. The rule is simple: fill the spool until it is nearly full when the fly line is wound on top. You want the spool diameter to be close to the reel frame diameter — that is when line speed is fastest and memory is lowest.
If you are unsure, check the reel manufacturer's specifications. Most list the backing capacity in yards for different fly line weights. Start with the middle of that range. You can always add more later if you find you need it.
Braided backing is the standard choice
Braided backing is made from woven synthetic fibers, usually nylon or polyester. It is thin (roughly 0.020 to 0.030 inches in diameter), very strong (20 to 40 pounds breaking strength depending on diameter), and does not absorb water. These qualities make it reliable in salt spray, cold water, and heat.
Braided backing comes in different weights and colors. Most anglers use 20-pound or 30-pound test. The difference is mainly diameter — 20-pound is thinner and lets you spool more yardage on a given reel. 30-pound is thicker and stronger, useful if you fish for large saltwater species or if your reel is small and you want maximum strength in less space.
Monofilament backing exists but is less common. It is cheaper and easier to handle by hand, but it absorbs water, stretches under load, and has more memory than braided. Most serious anglers avoid it. Dacron is an older braided material that still works well and costs less than modern synthetics, though it is harder to find.
Connecting backing to reel and fly line
Backing attaches to the reel spool with an arbor knot. This knot wraps around the spool post and cinches tight when you pull line. It is simple, reliable, and does not slip. Wind the backing around the spool post, tie an overhand knot around the standing line, then tie another overhand knot above it. Pull tight and trim the tag end.
Backing connects to the fly line with either a Bimini twist or a nail knot. The Bimini twist creates a loop-to-loop connection that is strong and easy to change if you swap fly lines. It takes practice but is worth learning. The nail knot is faster and creates a smaller connection, useful if you want a smooth transition through your guides, though it is permanent once tied.
Some anglers use a loop-to-loop connection by tying a loop in both the backing and the fly line, then threading one loop through the other. This is quick and reversible but creates a slightly larger knot that can catch on guides during casting. For most situations, a Bimini twist or nail knot is better.
Spooling backing onto your reel
You can spool backing by hand, but a mechanical aid makes it much faster and easier. A hand crank spooler holds the backing spool and lets you turn it with one hand while feeding line onto the reel with the other. A motorized spooler does the work for you — you just guide the line. Both are inexpensive and worth the investment if you spool multiple reels or fish often.
To spool by hand without a tool, have a friend hold the backing spool or place it in a bucket and feed line through your fingers while turning the reel handle. Keep tension on the backing so it winds tight and even. This works but is slow and tiring for 200+ yards.
Wind backing onto the reel under light tension — tight enough that it does not slip, but not so tight that you strain the spool. Once backing is on, attach the fly line with your chosen knot, then wind the fly line on top. Check that everything is secure before you fish.
When backing gets damaged or wears out
Backing can fray, weaken, or accumulate salt residue over time. If you fish saltwater regularly, rinse your reel with fresh water after each trip. This prevents salt from corroding the backing and reel frame.
If backing becomes visibly frayed or you notice a weak spot, cut out the damaged section and re-tie the ends with a surgeon's knot or Bimini twist. If more than a few yards are damaged, it is easier to strip everything off and respool. This is also a good time to inspect the reel spool for corrosion or damage.
Backing lasts many seasons if cared for. Most anglers replace it only when they change fly lines or when damage makes it necessary. Some saltwater anglers replace it annually as routine maintenance.
Backing for different reel sizes and species
| Reel Size / Species | Backing Weight | Typical Yardage | Why This Amount |
|---|---|---|---|
| Trout (small streams) | 20 lb braided | 50–75 yards | Most trout runs are short; extra backing is rarely used |
| Trout (large rivers, lakes) | 20 lb braided | 100–150 yards | Larger trout and faster water demand more line |
| Steelhead | 30 lb braided | 150–200 yards | Steelhead make long, hard runs; heavier backing handles the load |
| Saltwater (inshore) | 30 lb braided | 200–250 yards | Redfish, permit, and tarpon run hard and fast |
| Saltwater (offshore) | 30–40 lb braided | 250–300+ yards | Large tarpon, permit, and billfish demand maximum line |
Frequently Asked Questions
Do I really need backing for trout fishing?
Not always. Small trout in streams rarely run more than 80 feet, so your fly line alone may be enough. But backing fills the spool and improves casting, so it is worth adding even if you never use it. For larger trout in lakes or big rivers, backing is essential.
Can I use the same backing for different fly lines?
Yes, if you use a loop-to-loop connection. Tie a loop in the backing once, then tie loops in each fly line and connect them. This lets you swap fly lines without respooling. If you use a nail knot, you will have to cut and retie each time.
What happens if a fish reaches my backing?
Your backing is thinner and less visible than your fly line, so the fish may not notice the transition. Keep tension and let the fish run — backing is strong enough to land most fish. If the fish reaches the end of your backing, you will either break off or the fish will snap the line.
Does backing color matter?
Not for function. Bright colors (yellow, orange, white) make it easier to see how much line you have left during a fight. Dark colors are less visible to fish but this rarely matters since backing is thin and usually underwater. Choose whatever helps you see your line.
Can I use old fly line as backing?
Technically yes, but it is not ideal. Old fly line is thicker than braided backing, so you spool less yardage. It also has memory and may not cast smoothly. Braided backing is cheap enough that it makes sense to use the right material.