Fly Line Backing 101 (2021 In-depth Guide)

Lance Wilkins
Lance Wilkins
Editor @ CallOutdoors. Outdoor gear-head and adventure addict. I fish, camp and enjoy to writing about my adventures.


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Do you want to land that monster fish you’ve been dreaming about your whole life?

Fly line backing – what is it and do you need it?

These are all good questions to be asking and by the end of the article, you’ll know everything you want to know from the types to its purpose and the knots you should tie it on with.

What is fly line backing?

Blue Fly Reel Closeup
Blue Fly Reel Close Up

Fly line backing is a thin line that looks a bit like braid that goes onto your fly reel.

It comes in various breaking strains materials and colors all to match your fly fishing setup.

What is the purpose of fly line backing?

The backing is there so when a fish does take a long run, it stays connected to your reel so you can continue to fight it without losing it or running out of line.

When I was younger fly fishing for small trout I always wondered what fly line backing was exactly for.

Considering the fish I caught barely pulled the line off the reel, I thought it was there just to fill up the reel so the fly line was nearer the top. Boy was I wrong!

Better to be prepared

Whichever fly line you use, you probably have about 90-100 feet of it.

Now, what happens when you hook a monster trout or a bonefish in saltwater and the fish runs off with all your fly line?

Well, without some backing on your reel, that fish is going to break off, break your rod, or run away with your fly line.

All things you never want to happen!

Do you need fly line backing?

You could ask this question differently by saying – do you want to land that monster fish you’ve been dreaming about your whole life?

You 100% need fly line backing on your reel.

You may not see its benefit when catching 1lb trout as you can pull them in with just a tippet if you like.

But, when you hook that 15lb fish or ever go fly fishing in saltwater, your backing is what is going to ensure you land it.

What is fly line backing made out of?

Fly Reels
Fly Reels

There are two types of backing material out there; dacron and gel spun.

Each material is excellent for the backing but they do differ quite a bit and here is how.

They come in every color and I’d suggest you buy one with a color that is easy to see, so you can see where the fish on the end of your gear is.

Dacron Backing

Dacron is most commonly used as a staple fiber in clothes but when braided together into a line becomes an excellent backing material.

Dacron backing is strong, has low stretch for more feel, and is highly abrasion-resistant.

This makes it an excellent choice to put on your fly reel. Dacron backing is usually used for trout and small freshwater fishing as it’s relatively thick and will take up extra space on the spool.


Another thing to note about dacron is that it’s hollow meaning you can splice it to connect it to your fly line – more on that later.

Gel Spun Backing

Gel spun backing is made from braided polyethylene and has a smaller diameter but increased strength when compared to dacron.

The benefit of this is you can fit way more yards of gel spun on your arbor than dacron which comes in handy when you’re fishing saltwater for fish like sailfish or bonefish that can take you 200 yards into your backing in no time.


Gel spun has less stretch than dacron and is not hollow so you’ll need to tie a knot to connect to your fly line – which we’ll also discuss later on.

Where do you put the backing on your fly fishing gear?

Fishing with a Fly Rod with Yellow Line
Fishing with a Fly Rod with Yellow Line

The backing is the first bit of line that goes on to your reels meaning it sits underneath the fly line on the spool.

So before you put your fly line on your reel, you should make sure the backing is on the spool first.

How do you attach the backing to your fly line and fly reel?

There are a few different ways of doing this and it depends on the type of backing material you are using.

We’ll go in order starting with attaching it with knots to the spool, then winding it on, and finally attaching it to the fly line.

Which knots to use when tying backing onto the spool of your reel?

To start, you’ll need to remove your spool from the housing of your reel. Once removed, thread the backing through the housing first, so that you can wind it on later.

Once you have it set up, you can either use an Arbor knot or a Uni knot next to attach the backing to the spool.

Arbor Knot

How to Tie the Arbor Knot — Backing to Fly Reel Knot – Great for spinning reels as well

Uni Knot

LOOP Akademi ~ Uni Knot for attaching the backing on to the reel

The Uni knot has more strength overall but they are both fine as the idea is that a fish will never take you to the knot if you’re fishing correctly.


Make sure once tied, the knot and backing are super tight around the spool and hold it well so you can wind it on with a high amount of pressure in the next stage.

How to wind backing onto your fly reel correctly

The best way to check the backing is perfect on your reel is to give it a solid push once on and see if it’s soft or hard.

Soft backing is a big problem, especially with large saltwater species that will put you into the backing in less than a minute.

If your backing is soft then it will bite into itself meaning when a fish pulls it with much drag pressure, it’ll bite, get tangled, and ultimately break a connection.

This can end up in tears, arguments with your guide, and a lost fish.

Personal Experience

When I was guiding in Seychelles I put my client onto a big GT with just 5 minutes left of the day.

He cast, hooked up, we were on and in the backing, everything was perfect. That fish was ours, there was not much that could go wrong until the backing snapped due to an overwind.

Tears, shouting, and blame ensued – Please, make sure your backing is hard, 8!

Line Winder

No matter whether you’re using gel spun or dacron, the best way to put the backing on spools is with a line winder machine as it goes on level with the most amount of pressure.

If you can’t get to one, you’ll require a friend to hold your backing tightly while you slowly and meticulously wind it on with a lot of pressure.

How to tie backing onto your fly line

In the old days, everyone used to use a nail knot for the connection between the fly line and back but that was before fly lines came with loops.

These days you should create a loop in your backing to make it easier to add a new fly line when you want to swap it out.

When using gel spun, the best knot you can use is the bimini twist or a double bimini twist if you’re going after giants like tarpon or sailfish.

Bimini Twist

How to tie a bimini twist backing loop

Double Bimini Twist

How to tie a Doubled Bimini Twist ~ Backing and Braid Knot


The knots are complex and involve using both hands, your mouth, and a foot, but it creates a loop with the most strength around and you’ll like how easy it is to swap lines often.

If you’re using Dacron you can splice the fly line through it.

You’ll require a nail to open up the end of the dacron and then you can begin to thread the fly line up it, coming out every 0.5-1 feet and back in immediately.

Once you get 3-5 feet spliced you’ll get an extra tough connection.

How much backing should you have on your reel?

The short answer is – as much as possible while leaving enough space for your fly line to fit on top.

But, you’ll have to take into account reel size, backing diameter, and breaking strain, plus what species you’re fishing for.

On average, you’ll want 250 yards of 20 lb backing on most reels you’re using when freshwater fishing.

This much backing and in this size is more than enough to handle any run from trout, pike, bass, steelhead, or any other fish in fresh water.

Breaking Strain

Man Wearing a Blue Hat Fishing on a River
Man Wearing a Blue Hat Fishing on a River

Naturally, the breaking strain should go up along with the sizes of the species you’re fly fishing for.

Luckily the reel and arbor size go up when this happens too.

So instead of having 250 yards of 20 lb backing like you might for trout on a 4wt reel, you’ll have 250 yds of 80lb backing on a 12 wt reel for GTs.

How to check how much of what length and weight of backing your reel can handle

Every reel will often have a sign or icon that you can read close to the foot or high on the main housing that will indicate its capacity.

This capacity label tells you exactly what length and weight of backing you’ll require to fill your arbor while leaving space for the fly line – so you can go to the shop and buy the right amount.

A 4wt will say for example 200 yards of 20lbs while a 9wt might say 300 yards of 40lbs of backing. And luckily then usually sell it in those qualities and weights too.

Backing Out

Thanks for reading my article, I hope you enjoyed it and you now understand everything about backing and how to use it.

Please feel free to share the article around with your angling buddies who might be interested and check out some of our other articles on the site, we address everything in fly, deep, and spin fishing.


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Lance Wilkins
Lance Wilkins
Editor @ CallOutdoors. Outdoor gear-head and adventure addict. I fish, camp and enjoy to writing about my adventures.
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