When it comes to air filters, there are a variety of materials that can be used. The most common type and material used for almost all factory-produced cars is paper, foam, carbon, aluminum, steel, fiberglass, or plastic. This paper is a very compacted wood pulp that sticks together to form a much stronger material, which is then folded in the shape of a concertina to give more surface and is fixed to a rectangle of foam. It is cheap and effective, making it the go-to choice for many.
However, over time dirt will begin to clog the creases of the material, restricting airflow. This means that it will eventually have to be scrapped for a new one. The exact date you change it will vary depending on driving conditions, but you can generally expect a paper filter to last between one and two years or between 10,000 and 20,000 miles. Probably the first port of call for most people who change their standard filter is a cotton-based piece. They have layers of cotton gauze sandwiched between an aluminum mesh, providing a less dense material for air to penetrate than paper.
Since it's not as dense, in theory it should be less restrictive, allowing more air to enter and increasing power. However, any increase in power is likely to be small; a possible change in induction noise will be the only notable change in the driving experience. Cotton air filters can last the life of the car, although they need to be cleaned and re-greased once they are dirty enough. You must ensure that you do not lubricate the filter too much, as this can cause oil to penetrate the mass air flow sensor. Foam air filters are even less restrictive and use several layers of foam with different densities to stop contaminants, in addition to a wire mesh to help maintain the filter's shape.
The downside is that less restriction means it won't be as effective a filter, but in most conditions this is unlikely to cause engine problems. As with cotton filters, many use an application of oil to trap incoming dirt. Like cotton filters, it is possible to purchase one as a flat “panel filter” that fits inside the existing air box. Metal filters are made of stainless steel mesh layers and don't need to be greased. In addition, with larger gaps between the filter material, a metal filter will be less restrictive than cotton and foam designs.
However, once again with fewer restrictions there is less filtration. This design will naturally let more dirt through, although the particles are unlikely to be large enough to cause problems. Most likely, the engine or cabin air filter that comes with your car is a paper filter. Because the filter must be changed every 12,000 to 30,000 miles it's designed to be as affordable as possible. Woven wood pulp provides good airflow and at the same time reduces the amount of dust and dirt that can enter the engine and damage parts. Automatic paper filters are relatively inexpensive and are made to be discarded after each use.
Finally you can find a foam filter or filter wrap in the automotive filter replacement section of your local parts store. This is the least popular type of filter as foam doesn't offer the same capture capacity as paper and can restrict airflow. Foam is also the least environmentally friendly type of item. You'll often find foam filters on farm and lawn equipment. In many of these applications the foam part is coated with a special oil that increases the filter's ability to remove dirt.
If you live in a very dusty area your service center may suggest adding a foam filter wrap to your standard paper filter to help reduce the amount of dirt in the engine. Ultimately most drivers looking to take care of their daily driver will be satisfied with the cost and performance of a paper air filter. To improve long-term performance or for extreme conditions you may want to invest in a reusable cotton or foam air filter replacement. The shape of the unit can affect its performance as can its size: the smaller the area through which you are trying to introduce air, the more restrictive the configuration will be. If you've been looking for an air filter replacement for your vehicle you may have come across some that offer improved performance and others that offer more affordable prices. It is also possible to reduce restrictions by leaving the car's original airbox but then you have to think carefully about the location of the filter and the air supply that will be given to it with any new duct that is added. Some automatic cotton or gauze air filter replacements are designed to be cleaned, greased and reinstalled every 5,000 miles.
Many manufacturers apply a layer of oil that is supposed to help trap dirt particles instead of them accumulating in the filter material itself or passing to the engine. In high-performance vehicle applications, the air filter is designed to be cleaned and then coated with a special oil that increases its ability to capture more debris. The Medicaid (CMS) of 26% of Centers for Medicare provides funding for civil fines (CMP) to nursing homes in order protect indoor air quality during visits.
