Media filters can last up to a year before requiring to be changed.

What is a media air filter and how does it work?
A media air filter is a device which removes contaminants, often solid particles such as dust, pollen, mold, and bacteria from the air.

They are often used in internal combustion engines, gas compressors, diving air compressors, ventilation systems, and any other application where air quality is important.

The most common filters tend to be made with paper, foam, or cotton filters.  Some buildings, as well as planes and other man-made environments (e.g., satellites and space shuttles) use foam, pleated paper, or spun fiberglass filter elements.  Another method uses fibers or elements with a static electric charge, with attract dust particles.

Types of Air Filters
There are three main types of HVAC air filters: paper, synthetics and cotton.  Though all have varying degrees of practicality, it is generally recognized that cotton air filters are best because of their durability and technological advantages.

Paper
Paper filters are generally used in automobiles because they are inexpensive and disposable.  Due to the characteristics of paper, good airflow is sacrificed for good filteration.

An example of pleated-paper air filters designed for in-duct use with home heating, ventilation, and air conditioning (HVAC) systems is the 3M "Filtrete" line of products.

Synthetics
Polyester fiber is commonly used to make web formations used for air filtration.  Polyester has a high temperature rating (about 250 F) and is widely used in commercial, industrial, or residential applications.  Polyester can be blended with cotton or other fibers to produce a wide range of performance characteristics.  In some cases Polypropylene, which has a lower temperature tolerance, is used to enhance chemical resistance.  Tiny synthetic fibers known as micro-fibers are used in many types of HEPA (High Efficiency Particulate Air Filter) filters.

Many in-duct filters for home forced air heating and air conditioning systems are made from spun fiberglass fibers.  These filters are inexpensive, disposable, and come in various densities and sizes.  Less dense filters allow for higher airflow, but do not remove as much dust.  Higher density filters remove more particles, but are more expensive than pleated-paper filters for the same size.

Cotton
Cotton is generally regarded as the best material for air filters because of its excellent filtration and high airflow.  This is because the "holes" in cotton are much looser than paper, giving high airflow, but use concepts such as interception, impaction, and diffusion, which allow the fibers to filter particles much smaller than the actual "holes."  High performance air filters use oiled layers of cotton gauze.  Dust particles are held suspended in the cotton gauze actually "become" part of the filter medium to all the more increased filtration without obstructing airflow to the engine, thereby outlasting paper filters in service life and performance.