HEPA filters are a crucial component in air purifiers and are often mentioned in product descriptions. The abbreviation HEPA stands for "High Efficiency Particulate Air", which in German means "air filter with high effectiveness against particles". These filters are used in various applications to clean the air of the smallest suspended particles.

The way a HEPA filter works is based on a dense fiber network consisting of fine fibers and works similarly to a sieve, but with irregularly arranged fibers. This creates gaps of different sizes between the fibers through which air flows. The small particles in the air are trapped during this flow as they stick to the fibers of the net.

HEPA filters are standardized and are divided into different filter classes from 1 to 17, with a higher number meaning a higher filter performance for the smallest particles. Classes H13 and H14 are called HEPA filters and filter at least 99.9 percent of all dust particles larger than 0.1-0.3 microns. The separated particles include respirable dusts, mite eggs and excretions, pollen, smoke particles, asbestos, bacteria, various toxic dusts and aerosols.

It is important to note that HEPA filters can filter a wide range of particles from the air, including those that can be harmful to human health. Normal house dust, which is already larger and is separated by the pre-filter of an air purifier, is an example of this. Due to their high effectiveness and accuracy, HEPA filters are crucial for purifying indoor air, helping to improve air quality and reduce potential health risks.

To provide a better comparison, here are the filter ratings for particles sized between 0.1 to 0.3 micrometers: