Evaluation of Cloth Masks and Modified Procedure Masks as Personal Protective Equipment for the Public During the COVID-19 Pandemic | Infectious Diseases | JAMA Internal Medicine | JAMA Network
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    10 Comments for this article
    When Both Parties Where Masks During COVID-19 Pandemic.
    Gary Ordog, MD, DABMT, DABEM | County of Los Angeles, Department of Health Services, (retired)
    Thank you for the excellent article that supports protection by masks during the COVID-19 pandemic. Preferably, all parties are wearing PPE masks, which provides information for protection when all parties are protected. It is estimated that two parties each wearing an N-95 with 98.4% efficiency, would have a combined efficiency of 99.995%, which could provide protection against the minimum viral load required for infection. If both parties are wearing homemade masks that provide 80% efficiency, an estimated combined efficiency may to 96%, almost as good as the N-95 when used alone. Obviously, other preventative measures must be used as well.
    The conclusions are unsupported
    Mahmoud Ali, M.B.B.Ch. | Rutgers University
    The duration of test for each mask is 3 minutes only. Why is it too short? Ordinary people wear masks for hours. They commute and work while wearing the masks. What is the effect of time and prolonged usage? What is the effect of the reuse of the mask? Why didn’t the authors include more people with different races, sex and body size? What is the effect of walking or climbing stairs?
    3-layer Woven Mask or Knit Mask?
    Kat Preston |
    I have looked and looked on the Hanes website and see no 3-layer woven masks. I see one mask that looks identical to the one referred to as a woven mask in the study, but it is knit.

    Can the authors of the study please clarify?

    There is a huge difference between a knit cotton and a woven cotton used in masks.

    In addition,  two other masks used in the research look like knits (#1 and #3). As both these masks also come from sources that primarily manufacture knits, are they "woven" masks as stated?
    /> Other research has confirmed that the weave in woven fabric used in common consumer bandanas is not great for face masks. However, two to three layers and more tightly woven cotton such as good quality quilting cotton or higher thread count sheets, seems to offer good protection. This is what is most commonly recommended for people sewing masks in the community.
    Correction to the article? And a comment on the methods.
    Jeff Damir, BWEE, MSEE, MBA | SwaddleDesigns
    The researchers refer to a 3-layer cotton woven fabric mask. Unfortunately, the mask tested is a Hanes cotton "knit" fabric mask. 

    Hanes is known for their cotton "knit" masks. Other studies have shown that cotton "knit" fabrics are less effective than cotton woven fabrics for masks. Knit fabrics are not woven. 

    As experts recommend tightly woven cotton fabric for masks, hence, it is hard to understand why the researchers this particular mask. 

    I also question the decision to use 0.05 μm particles to test the efficacy of cloth, non-medical masks. 

    The test methodology using an 0.05 μm diameter particle is smaller than the size of the COVID-19 virus which is approximately 0.1 μm. Using a particle or smaller size is surprising, when researchers consistently talk about the airborne COVID-19 virus riding on droplets (5 μm) and aerosols (1 μm). 

    Testing the filtration efficiency of a cloth mask to stop a 0.05 μm particle may lead to false conclusions.  

    It would seem more relevant to test using larger particles of size 5.0 μm, 1.0 μm, and 0.5 μm. This approach would provide an understanding of how the mask perform related to droplets and aerosols, of interest.
    CONFLICT OF INTEREST: SwaddleDesigns is known to manufacture effective, secure and comfortable non-medical face masks
    Response to "3-layer Woven Mask or Knit Mask?"
    Phillip Clapp, PhD | University of North Carolina at Chapel Hill
    Thank you for your comment and query. The website description for the 3-layer cotton mask to which you are referring does not specify whether the fabric used in this product is made through a knitting or weaving process. After further inspection, it is apparent that the material in this mask is knitted and that we, therefore, incorrectly stated that this mask is made with a woven cotton fabric. We regret the error and have requested that the article be corrected.
    Response to "Correction to the article? And a comment on the methods."
    Phillip Clapp, PhD | University of North Carolina at Chapel Hill
    We appreciate your comments and clarifications. As stated in the previous comment, we erroneously referred to the material used in the 3-layer cotton mask tested in this study as “woven”. It is, in fact, made with a knitted fabric. This is important because, as you and the previous commenter have pointed out, cotton knit fabric is reported to be less efficient in filtering aerosols than cotton woven fabrics. We regret the error, and have requested that the article be corrected. 

    In regards to the aerosol composition of our test atmosphere, the exposure chamber was supplemented with NaCl particles using
    a TSI 8026 Particle Generator specifically made for respirator fit testing. This generator is commonly used to supplement ambient particle concentrations to allow for accurate fit testing of N95 respirators. Based on the mechanisms of particle deposition that govern filtration (i.e., diffusion, impaction, interception, and sedimentation), protection against aerosols of 0.05-μm particles would also confer similar or better protection against much larger aerosols or droplets, which, as you correctly state, are currently believed to be the predominant source for COVID-19 transmission.
    Thank you for prompt correction
    Kat Preston |
    Thank you for quickly looking into to the issue regarding the fabric in the 3 layer Hanes mask used in this research, promptly acknowledging the oversight, and requesting a correction to the article.

    Perhaps you can take on woven masks next! It would be wonderful to have some insight comparing the most common different patterns (that is, rectangular pleated, fitted with center seam, fitted folded center with darted nose/chin and 3D).
    Additional Clarification for Mask Construction
    Phillip Clapp, PhD | University of North Carolina at Chapel Hill
    We appreciate the additional comment from Kat Preston regarding the construction of masks pictured in Figures 1A and 1D in our article. While addressing the original comment we carefully inspected the construction of each mask tested and compared our findings with data provided by the manufacturers. The masks pictured in Figures 1A and 1D are indeed knitted and not woven. However, the manufacturer of the 2-layer nylon mask (Fig. 1A) states on their website, “masks are woven” and “...the specific weave used in the mask body has extremely high surface area for good filtration.” The manufacturer of the single-layer polyester/nylon mask (Fig. 1D) states on their website, “Our single layer masks are made with tightly woven Nightingale™ 200 needle material for the perfect combination of lightweight comfort and breathability.” The manufacturers of both masks appear to use “woven” as a generic descriptor for mask construction. We used the term "woven" in a similar fashion, which is incorrect.

    As previously stated, we regret the error and are working with the journal to correct references to “woven” throughout the article.
    Clarification of Figure 1A "Easy Mask" material composition
    Joel Steinberg, M.D. | Virginia Commonwealth University
    I enjoyed reading this important article. However, I would appreciate clarification of the following. According to the article, the cloth mask in Figure 1A (Easy Masks LLC) was a "2-Layer woven nylon mask" composed of "54% recycled nylon, 43% nylon, 3% spandex". However, when referring to the product's website, https://easymasks.com/products/apex-2-pack?variant=31641180405854 the color and fabric design of the mask in Figure 1A seem to match closely the "Apex" model, which according to the product website, is composed of "54% recycled polyester, 43% nylon and 3% Spandex". One of the other mask models offered for sale by this company, the "Eden" model, is composed of "54% recycled nylon, 43% nylon, 3% spandex", but this nylon model is not sold in the color/design of the picture of the mask displayed in Figure 1A of the article. Therefore, I am wondering if the tested mask as displayed in Figure 1A was actually the "Eden" model composed of 54% recycled polyester, 43% nylon and 3% Spandex, and not the Apex model composed of 54% recycled nylon, 43% nylon, 3% spandex.
    Response to Comment about the Cloth Mask in Figure 1A
    Phillip Clapp, PhD | University of North Carolina at Chapel Hill
    Thank you for your comment. In response to your query, we confirm that the data in the manuscript corresponds to a mask represented to us as the Easy Masks “Eden” model, which is described by the manufacturer as 54% recycled nylon, 43% nylon, 3% spandex. The specific Eden mask tested in our study was blue and black in color. However, that mask subsequently underwent material testing and was not available for photographing. Except for the color, the mask pictured in Figure 1A is identical in style and design to the mask we tested.
    Original Investigation
    December 10, 2020

    Evaluation of Cloth Masks and Modified Procedure Masks as Personal Protective Equipment for the Public During the COVID-19 Pandemic

    Author Affiliations
    • 1Department of Pediatrics, University of North Carolina at Chapel Hill, Chapel Hill
    • 2Center for Environmental Medicine, Asthma and Lung Biology, University of North Carolina at Chapel Hill, Chapel Hill
    • 3UNC Health Care, Infection Prevention Department, Chapel Hill, North Carolina
    • 4Center for Public Health and Environmental Assessment, US Environmental Protection Agency, Research Triangle Park, North Carolina
    • 5TRC, Raleigh, North Carolina
    • 6Duke Center for Antimicrobial Stewardship and Infection Prevention, Duke University, Durham, North Carolina
    • 7Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill
    JAMA Intern Med. Published online December 10, 2020. doi:10.1001/jamainternmed.2020.8168
    Key Points

    Question  What are the fitted filtration efficiencies (FFEs) of consumer-grade masks, improvised face coverings, and modified procedure masks commonly used during the coronavirus disease 2019 (COVID-19) pandemic?

    Findings  In this comparative study of face covering FFEs, we observed that consumer-grade masks and improvised face coverings varied widely, ranging from 26.5% to 79.0% FFE. Modifications intended to enhance the fit of medical procedure masks improved FFE measurements from 38.5% (unmodified mask) to as much as 80.2%.

    Meaning  Simple modifications can improve the fit and filtration efficiency of medical procedure masks; however, the practical effectiveness of consumer-grade masks available to the public is, in many cases, comparable with or better than their non-N95 respirator medical mask counterparts.


    Importance  During the coronavirus disease 2019 (COVID-19) pandemic, the general public has been advised to wear masks or improvised face coverings to limit transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, there has been considerable confusion and disagreement regarding the degree to which masks protect the wearer from airborne particles.

    Objectives  To evaluate the fitted filtration efficiency (FFE) of various consumer-grade and improvised face masks, as well as several popular modifications of medical procedure masks that are intended to improve mask fit or comfort.

    Design, Setting, and Participants  For this study conducted in a research laboratory between June and August 2020, 7 consumer-grade masks and 5 medical procedure mask modifications were fitted on an adult male volunteer, and FFE measurements were collected during a series of repeated movements of the torso, head, and facial muscles as outlined by the US Occupational Safety and Health Administration Quantitative Fit Testing Protocol. The consumer-grade masks tested included (1) a 2-layer woven nylon mask with ear loops that was tested with an optional aluminum nose bridge and nonwoven filter insert in place, (2) a cotton bandana folded diagonally once (ie, “bandit” style) or in a (3) multilayer rectangle according to the instructions presented by the US Surgeon General, (4) a single-layer woven polyester/nylon mask with ties, (5) a nonwoven polypropylene mask with fixed ear loops, (6) a single-layer woven polyester gaiter/neck cover balaclava bandana, and (7) a 3-layer woven cotton mask with ear loops. Medical procedure mask modifications included (1) tying the mask’s ear loops and tucking in the side pleats, (2) fastening ear loops behind the head with 3-dimensional–printed ear guards, (3) fastening ear loops behind the head with a claw-type hair clip, (4) enhancing the mask/face seal with rubber bands over the mask, and (5) enhancing the mask/face seal with a band of nylon hosiery over the fitted mask.

    Main Outcomes and Measures  The primary study outcome was the measured FFE of common consumer-grade and improvised face masks, as well as several popular modifications of medical procedure masks.

    Results  The mean (SD) FFE of consumer grade masks tested on 1 adult male with no beard ranged from 79.0% (4.3%) to 26.5% (10.5%), with the 2-layer woven nylon mask having the highest FFE. Unmodified medical procedure masks with ear loops had a mean (SD) FFE of 38.5% (11.2%). All modifications evaluated in this study increased procedure mask FFE (range [SD], 60.3% [11.1%] to 80.2% [3.1%]), with a nylon hosiery sleeve placed over the procedure mask producing the greatest improvement.

    Conclusions and Relevance  While modifications to improve medical procedure mask fit can enhance the filtering capability and reduce inhalation of airborne particles, this study demonstrates that the FFEs of consumer-grade masks available to the public are, in many cases, nearly equivalent to or better than their non-N95 respirator medical mask counterparts.