Which masks will protect you against SARS-CoV-2?

Researchers at University of Chicago used masks made of several different fabrics and tested their efficiency in filtering (keeping OUT) particles of TWO different size groups:

  • ~10 nanometer (nm) to 300 nm 
  • 300 nm to 6μm (micrometer)
    • Aerosols are under 5 μm.
    • Droplets are sized greater than 5 μm.

The scientific community is divided over whether SARS-CoV-2 spreads via aerosols, in addition to droplets. There are some who consider this dichotomy old-fashioned, and have used advanced tech to propose that particles leave the respiratory tract in the form of droplets and a turbulent gas cloud carrying a pay-load of various sized particles that can travel much farther than the 6 to 8 feet we think about! That’s a discussion for another post. For purposes of this post, I am going to use the terms aerosols and droplets.

  • Viruses such as Influenza and Respiratory Syncytial virus, both of which we see every single year, are spread primarily by droplets. It is thought that these don’t travel far and fall to the ground rather quickly.
  • Viruses such as Measles and Varicella Zoster Virus (cause of chickenpox) spread primarily by aerosols. It is thought that these may stay in the air for a few hours and continue to infect others. Measles is thought to be in air for at least 2 hours after infected person has left the room. To read an older blog post on measles, click HERE.

Why is it important to determine if spread of a virus occurs primarily via aerosols or droplets?

  • It tells us how far the virus can travel, once it exits the body in saliva and/or mucus laden droplets and aerosols.
    • These droplets and aerosols leave the body via coughs and sneezes or simply due to laughing, talking or even breathing.
  • Knowing whether virus travels mostly within aerosols or droplets (once it exits the body), also gives us an idea of how protective the different masks will be when it comes to preventing transmission of the virus.

See the Table below to get an idea of how effective some of the masks were in filtering particles of the two size ranges studied:

The researchers also found that openings and gaps between the edges of the mask and facial contours, reduces the efficiency of the masks in filtering (keeping OUT) these various sized particles. 

  • This stresses the importance of making sure the mask fits your face properly.

In an unrelated study from Northeastern University, Boston, researchers found that using a nylon stocking as a mask underneath the regular mask, enhances the fit of the mask, as well as improves filtration efficiency of the mask.

For those of you who can sew and want to make your own masks, please see the CDC recommendations below on how to do exactly that. For more information, click this LINK.

Please remember NOT to use masks on

  • children under age 2 
  • anyone who
    • has trouble breathing
    • is unconscious
    • is incapacitated or
    • is otherwise unable to remove the mask without assistance.

If you want to read the research papers on efficiencies of the various masks, see below for the links:

Wishing you continued safety during these times. Please remember to continue to engage in prevention measures. We are not in the clear, yet.