Choosing the right fly line can become one of the most tricky choices you have to make when it comes to the world of flyfishing equipment. With a plethora of options available,  let us walk you through how to choose the correct fly line and take the guess work out of the equation.

Fly lines have come a long way in 30 years and are unfortunately still one of the most overlooked items of gear. We touched on them in our previous blog on how to choose a fly rod, highlighting that the right line on a rod that is right for you will be a magical pairing, however, one can quickly make a R25 000 rod feel subpar by matching it with the wrong fly line. Consider the following before you buy your next fly line.

Grain or Weight

Just as every 7wt fly rod is not the same, every 7wt fly line will differ in both taper and grain weight. The grain weight of a fly line is measured by the weight of the head of the fly line or a portion thereof, this is important because you can either overload or underload your rod if the grain weight doesn’t correspond correctly. By overloading the rod, it will begin to feel heavy on your back and forward cast as the line straightens out, if you aerialise too much line, you run the risk of breaking your rod mid-cast. If you underload you rod, you won’t achieve the necessary bend in the rod which will translate into not feeling the cast, and not being able to cast as far. The reason we bring this up is because the label on the box indicating a ‘7-weight’ line, doesn’t automatically mean that specific line will be suitable for your 7wt rod. If you have a very fast (stiff) rod, then you might need to consider a power taper with is typically half a line weight heavier, and in turn will have a higher grain weight. Unfortunately, most single handed rods don’t indicate grain weight on the fly rod itself which can make selecting the right line a challenge. We would suggest relying on your guide or shop manager to help you make the ideal pairing here.

Line Density

Grain weight is separate to line density i.e. the sink rate of your fly line. You can have a 300 grain floating line and a 300 grain sinking line just the same, the sinking isn’t automatically heavier because it’s a sinking. Fly lines nowadays have countless options between straight densities (a full float or full sink line) and multi densities, such as an Airflo Forty Plus where your running line is either floating or intermediate and the head is a faster sink rate. This becomes important when fishing rivers, as a lighter density running line gives you the ability to still mend and manipulate your line, while being able to get your fly into the strike zone. We typically refer to density in either IPS (inches per second) or DI (density index), both of which indicate the same thing (i.e. the speed that it sinks).


A fly line is made up of various sections. The tip, the belly, and the running line. Starting from the back, the running line which makes up the longest part of the fly line has no taper to it. This slowly transitions into the belly which is where most of the weight of the fly line is, and is the thickest part of the fly line. The belly then tapers down into the tip of the line which is once again thinner than the belly. Combined, the tip and belly make up what is called the head of the fly line. This is where the magic is, and what determines the technical nuances of your line. A shorter more aggressive head is used when you want a line that will load your rod quickly thus minimizing false casts, and more often than not, achieve greater distance. A longer head that has less of an aggressive transition in taper lends itself well to a presentation line. Weighing up the difference between needing a line for distance and presentation should be your main focus when considering taper, and this is where you need to ask yourself where you’ll use this line and for what species. If you’re fishing Sterkfontein, Henries Fork or the River Test, then presentation should be your first focus. A line such as the Lee Wulff Triangular taper will be ideal in these cases because of the longer, thinner head. Most manufacturers will also offer a good all-round taper such as Airflo’s Universal taper. This will perform well in 80% of scenarios, but if you regularly fish larger flies into the wind, this is where a power taper will come in handy. When fishing for predatory fish, be it Pike in Sweden or Peacock Bass in the Amazon, an aggressive power taper will make it much easier to turn over that large double barrel popper, and also help you load the rod as fast as possible, helping reduce the number of false casts it takes to land that fly 25 meters away under an overhang.

Temperature Rating

Looking at the example of Pike and Peacock Bass, although you’ll need the same taper for both species, you’ll have to buy two very different fly lines. Every line has a temperature rating, either tropic, cold water, or all-round. Tropical lines are essential for destinations such as the Amazon, Seychelles, Lower Orange River, and Saudi. But if you were to head up north to Alaska, Norway or Russia; and likewise, down south to Patagonia, a cold-water line is a must. If you had to get this wrong, your tropical line will go stiff and become rigid in cold water, and your cold-water line will turn to spaghetti and become “sticky” in the tropics. Granted, these lines are more specialised by nature depending on where you do the bulk of your fishing. Most lines for trout are rated ‘all round’, they have a larger tolerance for varied water temperatures, but one also needs to consider not just the temperature of the water, but the ambient air temperature as well. An good example of this as if you’re going to be fishing from the deck of a boat that has been baking in the sun all day. All of these factors play a role in how your line will behave, either retaining its suppleness, making for easy casting and line management, or it will end up knotting time and time again which is the fastest way to ruin your day out on the water.

Core Strength and Core Material

Core strength is a minor consideration for most, but if you target large saltwater species such as Tarpon or GT’s, this does become important. Make sure your line is strong enough to get the job done, but what matters more is the material of your fly line core. Typically, you have two options: braid (i.e. ultra-high- molecular-weight polyethylene fibres) or monofilament (i.e.  nylon extruded in a single, continuous filament). Most lines use either a single mono strand or braided mono core, which is fine if you’re targeting smaller species and can use a bit of give in your line. However, the moment you start looking at a 7wt lines and heavier, we would highly recommend braided core lines. They have little to no stetch in them which aids in hook up rate, the ability to set the hook into the mouth of a tigerfish at 22 yards away, and of course more control when fighting a fish. There’s nothing worse than not being able to set a hook properly because your line stretches like a slinky! We’ve found that Airflo lines are built on some of the best braid cores, both in their trout lines which makes detecting takes that much easier, and of course all their heavier lines for bigger and more powerful fish.

The long and short of it is this, when you need to select a fly line, know where you’re going to use it. Once you know where and what species you’ll be catching, you’ll know if you need a cold water or warm water line, and can determine if you need something more aggressive or something that will give you the best possible presentation. Once you’ve established, what, where and why – then we would look at the weight of the line. Not just the indicated weight, but the grain weight. This is where the pairing between your rod and lines comes together, but can still be a bit of a guess. An expert will know how your rod will pair with different lines, if you have the luxury of being able to compare lines side by side on the same rod, do this, especially before a trip. The last bit of wisdom to leave you with is related to trips. If you’re going on a guided fly fishing trip, call the operator and ask them or their guides which lines they prefer best on that location. They’ve spent the weeks and years guiding the same piece of water and know what will be the most effective line to get the job done.