CDC Research Finds Double Masking Offers Better Protection Against COVID-19


Investigators also recommended a method of knotting and tucking in the sides of a medical mask, in order to minimize the leakage of air around the edges.

A new report published by the Centers for Disease Control and Prevention (CDC) has found that wearing a tight-fitting mask or wearing a cloth mask over a medical mask significantly limited the spread of severe acute respiratory coronavirus disease 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (COVID-19).

Universal masking is recommended to slow the spread of COVID-19, whether with a cloth mask or a medical mask, such as an N-95 mask. However, ensuring that these masks fit properly is key in order to prevent air from leaking around the edges. Investigators tried 2 approaches: layering a cloth mask over a medical mask and wearing a medical mask with knotted ear loops and tucked-in sides.

A knotted and tucked medical procedure mask can be created by bringing together the corners and ear loops on each side, knotting the loops where they attach to the mask, and tucking in and flattening the extra material in order to minimize the side gaps.

The report noted that other recent studies have examined the use of mask fitters to improve the fit of cloth and medical procedure masks. Fitters can be solid or elastic and are worn over the mask. The study results suggest that when fitters are secured over a medical mask, they can increase the wearer’s protection by 90% or more for aerosols in the size range considered to be the most important for transmitting SARS-CoV-2, according to the CDC.

Other studies have found that knotting and tucking a medical mask or wearing a nylon sleeve around the neck and pulling it up over the mask could significantly improve protection by fitting the mask more tightly to the wearer’s face. Double masking is another method to improve the fit of medical masks while maximizing the filtration properties of the materials they are constructed from.

The first CDC experiment examined how effectively various mask combinations reduced the number of particles emitted during a cough. According to the report, they assessed a 3-ply medical procedure mask alone, a 3-ply cotton mask alone, and the 3-ply cloth mask covering the 3-ply medical mask. They found that the unknotted medical procedure mask alone blocked 42% of the particles from a simulated cough, the cloth mask alone blocked 44.3% of the particles, and the combination of the cloth mask and the medical mask blocked 92.5%.

In the second experiment, investigators examined how effectively the 2 modifications to medical procedure masks reduced exposure to aerosols emitted while breathing. They used 10 mask combinations, including various configurations of no mask, double masks, and unknotted or knotted medical procedure masks. The experiment involved a cough simulator and an unmasked elastomeric headform to examine how the mask combinations impact those around the person coughing.

They found that adding a cloth mask over the medical procedure mask or knotting and tucking the medical mask reduced the cumulative exposure of the unmasked receiver by 82.2% and 62.9%, respectively. When the source of the cough was unmasked and the receiver was fitted with the double mask or the knotted mask, the receiver’s cumulative exposure was reduced by 83% and 64.5%, respectively.

Finally, when the source and receiver were both fitted with double masks or knotted masks, the cumulative exposure of the receiver was reduced by 96.4% and 95.9%, respectively.


Brooks J, Beezhold D, Noti J, et al. Maximizing Fit for Cloth and Medical Procedure Masks to Improve Performance and Reduce SARS-CoV-2 Transmission and Exposure, 2021 [news release]. CDC; February 10, 2021. Accessed February 10, 2021.

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