How Face Mask Filters Work

As wearing a face mask in public spaces has become compulsory in many countries worldwide, many different face mask types have become available to purchase. From respirator face masks to washable cloth masks and everything in between, there are many choices presented to buyers. 

With many choices comes many questions. 

In this article, we’ll tackle whether or not your face mask should have a filter, how a filter protects you, and more. 

This article talks you through the following:

  • How Face Mask Filters Work
  • Particle Filtration Efficiency (PFE): The Test To Look For In Protecting Against COVID-19
  • What about cloth masks with filter inserts? Pass on them.
  • How Does A Face Mask Protect You?
  • Choose A Face Mask With A Filter

How Face Mask Filters Work

Firstly, choosing a face mask with a filter adds a layer of protection to the wearer. 

When a person infected by COVID-19 breathes, coughs, sneezes, or speaks when wearing a face mask with a filter, a large number of their respiratory droplets containing viral particles are trapped by the filter.

Wearing the right face mask with a filter when sick effectively stops the spread of COVID-19.

That said, not all filters work the same, and mask materials are rated to filter out bacteria, viruses, or in some cases, nothing at all.

Particle Filtration Efficiency (PFE): The Test To Look For In Protecting Against COVID-19

There are two types of tests used to regulate masks:

bacterial filtration efficiency
particle filtration efficiency
  • Bacterial Filtration Efficiency: This test measures filtration of particles that are 3 microns or larger (the size of bacteria).
  • Particle Filtration Efficiency: This test measures particles’ filtration at the sub-micron level—meaning it measures the filtration of particles smaller than one micron. One example of a submicron is a particle put into the air from an aerosol can or a virus. PFE is the test that’s important to determine the right mask to use against COVID-19 because it’s a virus.

Knowing the difference between how masks are tested and rated is essential because while bacteria and viruses are both causes of infectious disease, bacteria are giants compared to viruses. 

To protect against COVID-19, make sure the mask is tested for Particle Filtration Efficiency. 

PFE is tested by securing the respirator down, blowing particles through it, then measuring how many particles transmit through the respirator. 

It’s important to note that these tests depend on having a good seal around the entire mask. 

Masks that filter 95% or more of the particulate during testing have a “PFE of greater than 95%”, which is the standard recommended for filtering out viruses. 

3-ply masks are tested based on Bacterial Filtration Efficiency, which means small particles can pass through the material. While they do provide some protection by stopping respiratory droplets from spreading, they do not provide a seal around the face and do not protect the person wearing them.

Let’s put this in another context: If your goal is to build a fence to keep out pests, the type of pest will determine your fencing. A fence made of wood with large slats could keep out a bear (bacteria), but it wouldn’t do much to keep out a mosquito (viruses).

Cloth masks are entirely unrated, neither BFE nor PFE. Because they’re made from various materials, it is impossible to tell what level of protection they provide.

What about cloth masks with filter inserts? Pass on them.

There are many cloth masks marketed as having filters with “PFE” or “BFE” ratings because there’s a small filter inserted into the cloth mask. 

They don’t tell you the filter is the only part of the mask that is tested. 

The air you inhale and exhale can enter and escape through the cloth mask’s fabric (and not just the filter itself). So, cloth masks do not provide adequate protection for the wearer or those around them. 

The protective facial portion of a valveless respirator, in contrast, is made entirely of material that’s proven to filter out viruses. 

When an infected person breathes, coughs, sneezes, or speaks, and the respiratory droplets containing viral particles land on the wearer’s mask, the filter will stop the virus from getting through to the wearer.

How Does A Face Mask Protect You?

Face masks, particularly PPE, such as respirators, are designed to protect the wearer from hazardous materials and substances such as bacteria, germs, and viral particles. 

The physical barrier provided by a face mask protects the wearer from direct contact with toxic or harmful materials and matter that may result in either infection or disease.

Wearing a face mask protects the wearer by reducing the transmission of germs, viruses, and bacteria. The face mask worn should always reflect the risks at hand, in conjunction with the likelihood of exposure. 

As important as choosing a suitable and appropriate face mask is wearing it correctly. Wearing a face mask incorrectly increases the likelihood of transmission and spread of infection.

Why You Should Choose A Face Mask With A Filter (But Not A Valve) 

Respirator face masks filter tiny particles, as small as .3 micron, up to 95%. Not only does a respirator face mask reduce the wearer’s exposure to large respiratory droplets such as bodily fluids, but it also reduces their exposure to tiny aerosol particles. 

While other filter face masks do not have the same effectiveness as the respirator face mask, wearing any mask is better than none at all. 

Learn more about respirator face masks here.

For more information on whether face masks can be the direct cause of health problems, read our previous blog post: What Health Conditions Do Face Masks Cause.

Cover photo by Anna Shvets from Pexels.