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What Are HEPA Filters?

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What Are HEPA Filters?

HEPA stands for High Efficiency Particulate Air and is used to describe air filters that can trap 99.97 percent of particles that are 0.3 microns. The HEPA standard was established in 1983. The micron size (0.3) is referred to by scientists as the MPPS, or the Most Penetrating Particle Size. Scientists have found that particles of that size evade typical air filters more than larger or smaller particles. HEPA filters were originally intended for use in lab and factory settings. Today, they are used in consumer products, including cars, vacuum cleaners, and air purifiers.

How do HEPA filters work?

Most modern HEPA filters consist of interlaced glass fibers that are woven in many directions to create a fibrous mesh. Particles are pushed and trapped into the filter and taken out of air circulation. So how does a HEPA filter trap particulates? There are several ways particulates are trapped.

Direct Impaction: Large contaminants, such as certain types of dust, mold, and pollen, travel in a straight path, collide with a fiber, and stick to it.


Sieving: The air stream carries a particle between two fibers, but the particle is larger than the gap, so it becomes trapped in the filter.

Interception: Airflow is nimble enough to reroute around fibers, but, thanks to inertia, particles continue their path and stick to the sides of fibers.

Diffusion: Small, ultrafine particles move more erratically than larger ones, so they’re more likely to hit and stick to fibers.


There are other filter technologies that work in concert with HEPA filters to trap many super-small contaminants, such as smoke, VOCs, and other chemicals. Activated carbon filters use small pores to capture some chemicals and odors that a HEPA filter might not catch.

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Are HEPA Filters Good for Allergies?

Dust mites, mold spores, pollen, and pet dander in the air inside your home can cause allergies or asthma problems. Using HEPA filters can trap these pollutants and may help bring allergy relief.

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Robert Sadowski

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