Air Filters

Air Filters and How They Work

Several filters work to keep components in your vehicle clean: cabin air filters, engine air filters, fuel filters, and oil filters are the most common. Your vehicle may have more, depending on its design.

What Is an Air Filter?

Two principal components in your vehicle need clean air: the passenger cabin and the engine. In both cases, the air filter removes dirt, grime, dust, pollen, and other impurities from air that has been drawn into the vehicle for your engine and the cabin.

Engine air filters (sometimes just referred to as "air filters") ensure your engine has clean air for efficient combustion.

Cabin air filters clean the air you and your passengers breathe. They trap many impurities from outside, including allergy-causing pollens and dust.

How Does an Air Filter Work?

An air filter is made of a medium that allows air through while catching particles that can contaminate air.

The surface often resembles an accordion, which increases the surface area and helps the filter trap much more than if the filter were flat. The accordion design also improves the filter's longevity, since it takes longer for pollutants and contaminants to clog it.

Particulate Matter

Minuscule liquid and solid particles suspended in the air are called particulate matter. Air filters help remove these from the air brought into a vehicle. However, filters are rated by the size of particulate matter (PM) they can trap.

Measuring PM

Particulate matter is so small that it's measured in micrometres (µm), often abbreviated to microns. One micrometre equals one-millionth of a metre. For scale, one strand of human hair is between 50 and 70 µm.

Whether an engine or air cabin filter, you will see a filter rating in µm. A PM2.5 rating means that the filter traps PM that measures 2.5 µm in diameter. The other common rating is PM10. The smaller the PM size, the cleaner the air. However, filters designed to trap PM2.5 can restrict airflow considerably. This is why you don't need an engine air filter that traps particles that small.

What Happens When an Air Filter Doesn't Work?

You know when windshield wipers work: your windshield is clear. When they don't work? You can't see a thing.

Air filters are a little different because they don't "announce" their presence. You only notice them when they malfunction, and even then, not always.

Why Does My Engine Need an Air Filter?

Your engine produces power by mixing air and gasoline and igniting the mixture. Should dirt, dust, and other contaminants enter the engine, they will cycle through, wearing away at engine components, often within a few thousand kilometres. Regularly changing your air filter helps avoid these problems and improves your engine's longevity.

The severity of a problem caused by a heavily clogged air filter depends on the age of your vehicle. Vehicles without computer controls would lose mileage.

However, the sensors in today's vehicles will adjust the air-fuel ratio caused by the reduced clean air so mileage is not noticeably affected. Many filters also have a bypass mechanism that prevents complete oil or fuel starvation. But when the filter is bypassed, the fluid is no longer being filtered and your vehicle isn't protected.

Do not be tempted to leave the air filter alone, though. With time, a clogged filter can become damaged and allow contaminants into the combustion chamber. Learn how to change your engine air filter here.

Why Do I Need an Air Filter for My Cabin?

Your vehicle will draw in air from outside, recirculate cabin air, or combine both sources of air. No matter the original source, you'll want it filtered.

An air cabin filter cleans air, so it's easier and safer to breathe. If air from outside entered directly into the cabin, you would inhale allergens, road dust, emissions, and more.

Read here for instructions on how to change your cabin air filter.

What Materials Is an Air Filter Made Of?

Different media have different properties, and not all media are available for each make, model, and purpose. We'll discuss the most common filter media here, but always speak with an automotive technician or one of our friendly advisors at your local NAPA Auto Parts store if you have any concerns.

Paper

The most common medium for air filters is paper. It performs well at a low upfront cost. However, the more contaminants the paper filter traps, the more it impedes air flow.

Your owner's manual or the instructions that came with the filter will explain how frequently you should change your paper filter. For the average daily driver in an average urban setting, annually is probably sufficient.

However, if you commute long distances or regularly drive down dusty roads, time your filter changes with your oil changes.

Foam

If you drive an off-road or small-engine vehicle or a motorcycle, you may prefer a foam filter. They're used for their ability to trap larger particles, like dust, while still maintaining airflow. You may also see them as a layer that wraps around a filter of another medium.

Cotton

You'll find cotton gauze on some styles of engine air filters. It's just as effective as paper and may be washable, but the upfront cost is higher.

Synthetic

Many filters may be a mix of synthetic materials that improve resilience to heat, chemicals, and moisture compared to paper filters.

Filter Fit and Type Matter Most

A filter's media matters in selecting a filter suitable for your vehicle and driving habits. However, the more important factor is the filter's fit. Check your owner's manual and use the vehicle finder at the top left of our website to ensure you only see products guaranteed to fit your vehicle.