Why do Fabric Masks Need to be Three Layers

We know now that wearing a face mask has become a critical part of not only controlling the spread of coronavirus but also keeping us protected from it. As the pandemic continues, researchers are now better understanding which specific masks work the best. For example, a study held at Duke University tested 14 different masks[1].

The study found that most of the masks were effective in reducing particle transmission, however, bandanas were ineffective, and masks made from fleece appeared to make transmitting the virus worse. That study’s results were backed by a previous study conducted by the World Health Organization[2] which stated that masks—homemade or store-bought—can help prevent the spread of the novel coronavirus—if they had three layers.

So why is a bandana, fleece mask, or a mask with less than three layers not as effective? Why do fabric masks need to be 3 layers?

What Do Masks Do Specifically?

Masks are a form of source control. As scientists and researchers have learned, up to roughly 40% of people infected with the virus that causes COVID-19 may experience little to no symptoms. Meaning, whenever they talk, cough, or sneeze they can still spread the virus to others in the form of respiratory droplets expelled into the air. These droplets then evaporate into fine particles that can linger. Wearing a mask traps these larger respiratory droplets before they can evaporate.

Wearing a mask regularly can prevent spreading at the source, even when we don’t know we’re sick.

Why a Single Layer of Fleece or Polyester Won’t Work

The study from Duke University featured experiments using medical-grade masks, and single-layer bandanas, handkerchiefs, and fleece balaclavas (cold-weather gear that covers the entire face except for the eyes) as well as neck gaiters (tube of performance fabric typically used for running outside), and concluded that they, unfortunately, offered little protection. Meanwhile, N65 respirators, surgical masks, and homemade cloth masks performed much better.

For these experiments, researchers in the Duke Department of Physics positioned a laser beam in a dark box that would illuminate any respiratory droplets as they passed through the light. They positioned a person wearing their mask over their mouth by a hole in the box. The speaker then said a phrase while a camera on the other end of the box captured video of droplets in real-time. Participants spoke the same three words, five times into the laser, “Stay healthy, people.”

The single-layer masks or single-layer coverings which were made from polyester spandex material performed the worst in the case study. It was found to be producing even more particles when worn than what would be produced without a mask being worn. The polyester textile used alone was attributed to taking the larger respiratory droplets and making them into even smaller particles—and did not prevent those particles from escaping. As the particles were even smaller, this makes them much easier to hang around longer in the air, carried away easier in the air, and most likely means it was counterproductive to even wear a single layer mask made from that material.

Why Your Mask Needs to be 3 Layers

The World Health Organization recommends now that anyone going out in public for any reason wear a three layer face mask. If you are 60 and over, or have underlying health conditions if possible, you should wear a medical mask in situations where physical distancing isn’t feasible.

The WHO in June 2020, released masked guidance that goes into specific details about what exactly a three-layered fabric mask should be made of[3] :

  • An inner layer of absorbent material. For example, cotton.
  • A middle layer. The middle layer should act like a filter or barrier, made of non-woven material such as polypropylene.
  • An outer layer of a non-absorbent material, such as polyester or a polyester blend.

WHO also suggests avoiding stretchy materials as materials that can stretch have very poor filtration abilities and are sensitive to being washed at high temps. Besides, it’s important to make sure your mask fits or still fits closely over your nose, cheeks, and chin. When the edges of your mask do not touch your face or begin to lift away, unfiltered air can seep into the mask as well as out of it.

The reason why your mask needs three layers is to better protect yourself as well as protect those around you from any chance of escaping particles. A 3-layer homemade mask using the right materials with the right fit is one of the safer measures to help stop the spread of the virus to others and to help protect yourself.

  1. https://advances.sciencemag.org/content/6/36/eabd3083
  2. https://www.who.int/emergencies/diseases/novel-coronavirus-2019/advice-for-public/when-and-how-to-use-masks
  3. https://www.who.int/publications/i/item/advice-on-the-use-of-masks-in-the-community-during-home-care-and-in-healthcare-settings-in-the-context-of-the-novel-coronavirus-%282019-ncov%29-outbreak