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Air Filter Choice: which is best for you?

We’ve introducing an extra choice for both buyers of new intakes, and existing intake owners – you can now select between our current Trifoam filter or our new Pleated Cotton filter unit.

We’re pretty proud of the performance of our race-bred intake systems, and for good reason. This choice of filter materials gives more options to owners. Both filters are completely interchangeable with one another. Got an existing RacingLine Intake? Then you can choose either filter to fit it. Buying a new Intake?

So the only choice left - which filter is right for you?


Really, it all comes down to this: both of our filter options are market-leading high performance, carefully designed and tested filters with huge surface area that will work beautifully in your RacingLine Intake. We wouldn’t sell a filter material that didn’t.

If you are the type of owner to fit your intake then not open it again, our Pleated Cotton is the filter for you and will give you years of trouble-free high performance motoring. Add in the Cotton Filter 'Oversock' option and you'll have even more protection from the dirt that will eventually settle in the filter surface.

But, if you want the maximum power for the maximum time, if you’re a keen racer or a dyno warrior and you’re happy to invest a little time cleaning and reoiling your Trifoam filter, it is definitely the way to go.

You’ll be happy either way!



Your engine needs huge amounts of clean, fresh air to deliver the sort of power outputs that a modern TSI is so capable of. But just as important as the airflow, it’s absolutely critical to keep all dirt out of the engine's precise and vital inner workings.

Imagine running your engine without a filter for thousands of miles. Performance would be great, but small dirt particles will gradually cause engine wear which leads to loss in performance, efficiency and eventually, engine failure. Think of it like sand paper dragging across every little part in your engine eventually wearing down things like piston rings, valve seats and bearings, killing power and efficiency. No one wants that!

So at the risk of stating the obvious, a filter needs to find a balance between filtering dirt out of the air, yet still allowing plenty of air to flow into the engine. That’s why the filter is so, so critical. Think of it as very heart of your intake.



Your car will have come from the factory with the OEM paper filter. It’s simple, effective, and above all, cheap. But paper is not efficient.

Because you are reading this, you’re probably already interested in improving your car’s breathing by improving its airflow. A RacingLine intake is the obvious choice - but this is where your filter choice begins.

Really, the only two credible choices for a performance intake is a filter media of either foam or cotton.

The first thing to understand is that filters have to stop dirt by either blocking it or catching it – in other words, trapping it on the surface, or capturing it deeper inside the filtration media.

It’s often a surprise to people to understand that almost all filter materials tend to flow about the same as each other (for a given surface area) when brand new. It’s only when the filter gets dirty that the huge differences come in.

The next thing to consider is that the largest possible filter should always be selected to ensure the greatest surface area to cause the least pressure drop.

By increasing the surface area, the pressure drop value is decreased - meaning more free-flowing clean air can enter the inlet system, thus increasing volumetric efficiency of the engine.

Pleated Cotton filters will always have more overall surface area than a dimensionally identical foam filter. This is due to the nature of construction of the pleat pack - being meticulously folded in a ‘zig-zag’ shape, compared to a foam filters’ uniform smooth profile.

At first this may seem a major advantage for the Pleated Cotton from a filtration point of view. However, the larger cross-sectional depth area of the foam makes up for the lower surface area because it arrests various size dirt particles throughout the layers of foam, whereas for pleated filters the filtration is undertaken on the surface of the pleat pack, with little room for particles to displace through the filtration media.



For the past decade, since we launched our intake range, we’ve only offered the Trifoam filter? Why? Well, we know that it’s simply the most effective form of filtration available, combining the best possible balance between the protection from dirt that your engine needs, with the maximum possible level of airflow needed for big power gains.

But it’s a motorsport part – and as with all motorsport parts, you’ll need to commit to a regular programme of maintenance – as cleaning and reoiling it regularly will return it to brand new performance each and every time.

Yet we know that not everyone wants to take on this sort of maintenance. Many owners prefer to ‘fit and forget’ a more robust filter. So we have launched this alternative that’s easier to live with – our new Pleated Cotton filter unit.

Both are great filters, and both will delight you for many years. There’s no right or wrong choice here; rest assured that we just wouldn’t offer a product that wasn’t right.

This article is about helping you to decide which of these great options is best for you.


Let’s start by looking at our Trifoam triple layer foam filter unit in more detail. Three difference densities of foam are bonded together into large sheets, then cut into shape by hand and bonded over a plastic ‘cage’ to form the shape.

Our love of this foam material comes from needing to specify the very best induction materials for our race programmes over the past 20 years. And we’re not alone in this view – if you look at how many top-level motorsport teams around the world (including World Rally, WEC and even F1, plus nearly every single performance off-road vehicle in the world) currently use this foam filter material, it speaks for itself.

The first reason for our preference for foam is its dust load up tolerance, which is far superior to cotton or paper. In the industry, our Trifoam is known as a ‘multilayer depth loading media’. What does that mean? When dust is fired into the material, it is trapped throughout the depth of the foam - so keeping the airpaths open for longer rather than collecting it on the surface.

By contrast, cotton filters (and also the factory paper filters) are called a ‘surface loading media’, meaning that all the dirt accumulates on the surface of the filter, slowly blocking the airpaths.

Get your microscope out, and you’d see that the foam has a much larger cross-section and therefore many more places for the dirt to stick to through its depth. It also is much more open which is great for airflow. The large open cross-section has completely random passages through the ‘bubbles’ in the foam, so the air can't go straight through it. Of course, the dirt can't go straight through it either, which is how the dirt gets trapped deep inside the filter.

All of which means that the Trifoam filter can deal with much more dust and essentially give better performance for longer in most environments.

There’s more to consider too...foam filters weigh a fraction of a cotton equivalent. Also the ‘dome’ design that we use means a huge increase in the surface area. Rather than many designs that use an end-cap on the filter, the open end of our Trifoam filter is all usable filter material. And a filter is all about that surface area.

This all sounds just perfect. Decision made?

Hold on, as there is always a compromise! Foam is a relatively delicate material, one that really needs its owner to give a little bit of love to maintain it. The secret to keeping the Trifoam filter at its peak performance is to regularly clean and reoil it (using our branded cleaner kit). Do this, and it will return to as-new condition each time. Neglect it, and eventually it will dry out and deteriorate.

So if you race your car, or always want the very best airflow all of the time, the Trifoam is the filter unit for you.

Considerations for the Trifoam filter:

  • the best possible airflow for better performance

  • airflow barely deteriorates with dust-loading

  • foam is more delicate and does need TLC

  • after cleaning and reoiling them they’re as good as new

  • they are a lightweight carefully designed genuine motorsport filtration solution


So there are a lot of good reasons to choose the Trifoam filter. But what about the new Pleated Cotton filter?

First and foremost, it’s an extremely robust and very long-lasting filter - but still with excellent flow characteristics and minimal initial pressure drop.

Ultimately, a filter’s performance is all about surface area. The deep pleats on our cotton filter clearly increase the surface area whilst the epoxy coated mesh encapsulates the cotton with an incredibly durable outer layer.

It’s constructed from three layers of extremely fine-weave cotton, bound tightly top and bottom by the mesh. The material is then pleated and hand-formed into shape. By increasing surface area, these pleats increase its filtering ability and increase its dirt holding capacity. The mesh provides the support to stop the media get sucked into the engine and also makes for a durable outer layer to protect against larger debris.

When they are clean, both filters are almost identical in performance.

The initial pressure drop figures we have recorded are just as good, and as far as power and torque are concerned the difference is near enough negligible.

So you may now be thinking this is any easy choice for the Pleated Cotton.

However, once again, there is a compromise. Any Pleated Cotton Filter material will ultimately block up faster If you throw a lot of dirt quickly at the face of it (such as following another car along a dusty road). All this dirt will start to accumulate on the surface of the filter, and gradually block it up - eventually restricting engine power as the filter efficiency drops.

As dirt tries to pass through it, it first starts to build up at the bottom valley of the pleats, and slowly builds up towards the peaks. It’s not dangerous for your engine at all, as it’s still providing full filtration. But gradually you may start to notice that performance is not what it once was – and that’s ideally the time to replace your filter unit (of course, we supply both types as filter-only, making this an easy serviceable item).

Remember how the Trifoam filter does a much better job of capturing this dirt throughout its depth, still leaving a good path for the air to pass through efficiently?

Basically, the Pleated Cotton gets restrictive earlier, whilst the foam remains very open.

There are other advantages to our design of Pleated Cotton filter too. All the other cotton filters on the market tend to use a heavy PU clamp-on style design; ours continue to use a giant air horn/ram pipe just as the Trifoam design does - offering definite advantages over the competition. It marginally reduces weight and allows easy connection to either the factory turbo inlet hose pipework or to our silicone pipe upgrades with beautiful smooth airflow guaranteed.

So what’s the reason to choose the Pleated Cotton filter?

  • Extremely robust and very long lasting

  • Excellent flow characteristics when new

  • No cleaning needed – fit and forget

  • Giant surface area and air horn into the pipework

  • Beautiful looking!


If the Pleated Cotton filter is your choice, you have one more option to consider.

The RacingLine 'Oversock' simply slides over the top of your Cotton Air Filter. The single layer foam material protects debris and dust from settling on Cotton Filter surface. It's very common in motorsport uses, especially for off-road racing to provide this outer protection layer.

When it comes to time to service your car, simply slide the oversock off and clean it, or even replace it.

Underneath it, you'll see how it keeps the surface of your Cotton Filter airflow like new. Because Cotton Filters of any type always deteriorate in efficiency as dirt settles and slowly restricts airflow - this oversock keeps the surface clean and performing perfectly.

Check out the photo below. We use our standard dust-loading tests (as we do on all our filters) to test filter efficiency by firing fine dust through each unit for a prolonged period. Here, the left-hand filter was tested with Oversock fitted (then removed for photo). The right-hand filter did not have an Oversock. You can see that the

RH filter did a great job of containing the heavy dust, but has now got a layer sitting on its surface. The LH unit's surface is almost completely clean under the Oversock.

Our dust-loading test : LH filter had Oversock fitted for the dust test (then removed for photo), RH filter did not
After dust-loading test : LH filter had Oversock fitted, RH filter did not


As we’ve said, the secret to keeping the Trifoam Filter at its peak performance is to regularly clean and reoil it (using our branded cleaner).

Clean and reoil your foam filter regularly, and it will literally return to as-new airflow each time.

Having said that, foam is a delicate, motorsport inspired material. We have seen failures of the foam if it’s neglected and the oil dries out, or if it’s cleaned with the wrong materials, or not reoiled. Let any of this happen, and it will turn dry and may well deteriorate significantly.

It’s very simple with any brand of Pleated Cotton filter. Once this material is dirty you are really upsetting the structure of the cotton by attempting to clean it. Once it has been washed a couple of times it really starts to break down, and loses its ability to filter the dirt so effectively. So, you can clean and re-oil a cotton filter, we really don’t recommend cleaning them - it's always much better to replace the filter unit.

Our guidance:


* Inspection every 10,000 miles / 16,000 kms - check its clean

* Replace (or service) every 40,000 miles / 60,000kms


* Visual inspection every 6 months - check its clean and still oiled

* Clean & Reoil every 10,000 miles / 16,000 kms



Before we even consider filter life, it's really important to understand that the conditions you use your car in makes a huge difference to filter life and maintenance schedules.

Drive in dry, dusty conditions, and you'll need to clean and/or replace your filter much more frequently. Drive in damper, clean air with less dust and the filter will last for much longer without attention.

A Pleated Cotton filter can be extremely hard wearing and durable, but cleaning can be detrimental to its dust arresting characteristics. When you clean a Pleated Cotton filter, some of the cotton’s molecular structure is lost. At first glance, this can often be overlooked due to it becoming more free-flowing – but in fact, it is reducing the filtration efficiency of the unit – which is the main purpose of an air filter. A Pleated Cotton Gauze filter can be extremely hard wearing but in harsh dusty environments this is dramatically reduced.

Contrastingly, foam filters are not damaged during the cleaning process and all dirt is easily removed if done thoroughly, leaving the filter as clean is it was when it left the factory. The main risk of decreasing filter life of foam filters is letting the filter oil dry out. Therefore, it is very important to ensure the filter is cleaned and re-oiled in accordance with usage guidelines. If the oil drys out of the foam, it makes it very brittle and may cause pieces of the filter to decompose. However, if the filter is frequently cleaned and re-oiled using the correct procedure; this will be prevented, and the Trifoam filter element will perform as new for many years.

In summary, if you are after a ‘fit and forget’ approach to your air filtration solution, the Pleated Cotton filter would be the optimum choice. However, if you are willing to maintain your filter in regular service intervals, then the benefits of a Trifoam filter are superior.

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