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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Figure 1.  Consumer-Grade Masks and Improvised Face Coverings
Consumer-Grade Masks and Improvised Face Coverings

The face coverings tested in this study included a 2-layer woven nylon mask with ear loops (54% recycled nylon, 43% nylon, 3% spandex), tested with and without an optional aluminum nose bridge and nonwoven filter insert in place (A), a cotton bandana folded diagonally once “bandit” style (B), a cotton bandana folded in a multilayer rectangle according to the instructions presented by the US Surgeon General (C), a single-layer woven polyester/nylon mask (80% polyester, 17% nylon, 3% spandex) with ties (D), a nonwoven polypropylene mask with fixed ear loops (E), a single-layer woven gaiter/neck cover balaclava bandana (92% polyester and 8% spandex) (F), and a 3-layer woven cotton mask (100% cotton) with ear loops (G).

Figure 2.  Medical Procedure Mask and Modifications Designed to Enhance Mask Fit or Comfort for the Wearer
Medical Procedure Mask and Modifications Designed to Enhance Mask Fit or Comfort for the Wearer

A medical procedure mask with ear loops (A) was modified by tying the ear loops and tucking in the side pleats (B), attaching ear loops to a 3-dimensional–printed “ear guard” (C), fastening ear loops with a 23-mm claw-type hair clip placed behind the wearer’s head (D), placing a ring of 3 ganged rubber bands over the mask and around the wearer’s ears (E), and sliding a 10-inch segment of nylon hosiery over the fitted procedure mask (F).

Figure 3.  Evaluation of Fitted Filtration Efficiency (FFE) Using the US Occupational Safety and Health Administration Modified Ambient Aerosol CNC Quantitative Fit Testing Protocol for Filtering Facepiece
Evaluation of Fitted Filtration Efficiency (FFE) Using the US Occupational Safety and Health Administration Modified Ambient Aerosol CNC Quantitative Fit Testing Protocol for Filtering Facepiece

The overall FFE for a medical procedure mask with ear loops (A), medical procedure mask with the ear loops tied and mask corners tucked against the wearer’s face (B), and 2-layer woven nylon mask with an aluminum nose bridge and 1 nonwoven filter insert (C) was 38.5%, 60.3%, and 74.4%, respectively. Particle penetration (y-axes) is defined as particle concentration behind the mask expressed as a percentage of the ambient particle concentration and is calculated during repeated-movement tests (bending at the waist, reading aloud, looking left and right, and looking up and down). The overall percentage of FFE is defined as 100 × (1 − behind the mask particle concentration / ambient particle concentration). Overall FFE percentage and SD were calculated across the length of the test. L/R indicates left/right; U/D, up/down.

Table.  Face Mask FFE Against Submicron Particle Penetration
Face Mask FFE Against Submicron Particle Penetration
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    10 Comments for this article
    EXPAND ALL
    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.
    CONFLICT OF INTEREST: None Reported
    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?
    CONFLICT OF INTEREST: None Reported
    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.
    CONFLICT OF INTEREST: None Reported
    READ MORE
    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
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    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.
    CONFLICT OF INTEREST: None Reported
    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.
    CONFLICT OF INTEREST: None Reported
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    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).
    CONFLICT OF INTEREST: None Reported
    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.
    CONFLICT OF INTEREST: None Reported
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    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.
    CONFLICT OF INTEREST: None Reported
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    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.
    CONFLICT OF INTEREST: None Reported
    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.

    Abstract

    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.

    Introduction

    Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of coronavirus disease 2019 (COVID-19), is a transmissible virus that infects the upper and lower respiratory tract,1 leading to a high viral titer in saliva and respiratory secretions.2 A key public health control strategy for mitigating SARS-CoV-2 transmission is use of masks or face coverings by the public.3 Masks that completely cover the nose and mouth are effective at reducing seasonal coronavirus and influenza transmission when worn by infected persons4,5 and noninfected persons who may come into contact with infected individuals.6,7 This is supported by emerging epidemiologic data that indicate that community-wide use of masks can effectively contribute to the prevention of SARS-CoV-2 transmission.8

    As the adoption of face coverings during the COVID-19 pandemic becomes commonplace, there has been a rapid expansion in the public use of commercial, homemade, and improvised masks that vary considerably in design, material, and construction. Similarly, the press and social media outlets have reported on numerous innovative “hacks,” devices, and modifications (enhancements) that claim to improve the performance characteristics of conventional masks (typically surgical or procedure masks). Despite their widespread dissemination and use during the pandemic, there have been few evaluations of the efficiency of these face coverings or mask enhancements at filtering airborne particles. In this study, we used a recently described methodological approach9 based on the Occupational Safety and Health Administration (OSHA) Fit Test to determine the fitted filtration efficiency (FFE) of various consumer-grade and improvised face masks, as well as several popular modifications of medical procedure masks.

    Methods
    Testing Procedure

    Fitted filtration efficiency tests were conducted between June and August 2020 in a custom-built exposure chamber (US Environmental Protection Agency Human Studies Facility in Chapel Hill, North Carolina) as recently described.9 The institutional review board at the University of North Carolina at Chapel Hill waived the need for study approval as well as individual consent needed for device testing. Briefly, a TSI 8026 Particle Generator was used to supplement the chamber with sodium chloride (NaCl) particles that had a count median diameter of 0.05 μm (range, 0.02-0.60 μm) as measured by a scanning mobility particle sizer. The test atmosphere was allowed to stabilize for 30 minutes before FFE testing. The chamber temperature and humidity during testing ranged from 73.4 °F to 85.1 °C and 10% to 50%, respectively. The test atmosphere used for this study reflects typical indoor conditions, with exposure to small particles that are slightly smaller than individual SARS-CoV-2 virions (reported to range between 0.06 μm and 0.14 μm10). A sampling port was installed in each mask using a TSI model 8025-N95 Fit Test Probe Kit to allow sampling behind the mask. All masks were fitted on a man (weight, 165.3 lb; height, 5 ft and 10.1 in; head size, 23.0 in) with no beard. A pair of TSI 3775 Condensation Particle Counters were run in single-particle analysis mode to continuously monitor ambient particles (0.02 μm-3 μm) in the chamber just outside the face mask and particles in the breathing space behind the face mask at a sampling rate of 1 second.

    Fitted filtration efficiency measurements were collected during a series of repeated movements of the torso, head, and facial muscles as outlined by the OSHA Quantitative Fit Testing Protocol (Modified Ambient Aerosol CNC Quantitative Fit Testing Protocol For Filtering Facepiece Table A–2—RESPIRATORS). The FFE corresponds to the concentration of particles behind the mask expressed as a percentage of the particle concentration in the chamber air, and was measured for the duration of each test described in the OSHA protocol (bending at the waist, reading aloud, looking left and right, and looking up and down). The overall percentage of FFE is calculated as 100 × (1 − behind the mask particle concentration / ambient particle concentration), and the percentage of FFE and the standard deviation were calculated across the length of the test. The total testing time for each mask was approximately 3 minutes.

    Products Tested

    Two categories of products were tested for this study: consumer-grade face masks and medical procedure masks with and without enhancements. The following consumer-grade masks were tested (Figure 1): (1) a 2-layer woven nylon mask (54% recycled nylon, 43% nylon, 3% spandex) with ear loops (Easy Masks LLC) tested with an optional aluminum nose bridge and nonwoven filter insert in place (Figure 1A), (2) a cotton bandana folded diagonally once “bandit” style (Figure 1B) or in a multilayer rectangle according to the instructions presented by the US Surgeon General (Figure 1C; https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/how-to-make-cloth-face-covering.html), (3) a single-layer woven polyester/nylon mask (80% polyester, 17% nylon, 3% spandex) with ties (Renfro Corporation) (Figure 1D), (4) a nonwoven polypropylene mask with fixed ear loops (Red Devil Inc) (Figure 1E), (5) a single-layer woven gaiter/neck cover balaclava bandana (92% polyester and 8% spandex; MPUSA LLC) (Figure 1F), and (6) a 3-layer woven cotton mask (100% cotton) with ear loops (Hanesbrands Inc) (Figure 1G).

    The baseline FFE of unmodified medical procedure masks with elastic ear loops (Cardinal Health Inc) was measured (n = 4) and compared with the FFE of the same type of mask with various modifications designed to enhance its function (Figure 2). The following modifications were tested: (1) enhancing the mask/face seal by tying the ear loops and tucking in the side pleats (Figure 2B; https://youtu.be/UANi8Cc71A0), (2) fastening ear loops behind the head with 3-dimensional–printed ear guards (Figure 2C; https://www.thingiverse.com/thing:4249113), (3) fastening ear loops behind the head with a 23-mm claw-type hair clip (Figure 2D), (4) enhancing the mask/face seal by placing a ring of 3 ganged rubber bands over the mask, with the center rubber band placed over the nose and chin of the participant and the left and right side bands looped over each ear (Figure 2E; “fix-the-mask” 3–rubber band method https://www.youtube.com/watch?v=CVjGCPfRwUo), and (5) enhancing the mask/face seal by sliding a 10-inch segment of nylon hosiery over the fitted mask (Figure 2F).11

    Results

    This study evaluated the FFE of 7 consumer-grade masks and five procedure mask modifications. The mean (SD) FFE of consumer-grade face masks tested in this study ranged from 79.0% (4.3%) to 26.5% (10.5%), with the washed, 2-layer woven nylon mask having the highest FFE and the 3-layer woven cotton mask having the lowest. The cotton bandana folded into a multilayer rectangle affixed to the ears with rubber bands, as described by the US Surgeon General, provided a mean (SD) FFE of 49.9% (5.8%). Folding the bandana bandit style produced a similar result (mean [SD] FFE, 49.0% [6.2%]). The tested mean (SD) FFE of the single-layer woven polyester gaiter/neck cover balaclava bandana was 37.8% (5.2%). The single-layer woven polyester/nylon mask, which is attached with tie strings, tested at a mean (SD) FFE of 39.3% (7.2%). The nonwoven polypropylene mask with nonelastic (fixed) ear loops tested at a mean (SD) FFE of 28.6% (13.9%).

    As expected based on data from our previous work,9 a National Institute for Occupational Safety and Health–approved 3M 9210 N95 respirator used as a reference control provided very high mean FFE (98.4% [0.5%]; n = 1) (Table). The medical procedure masks with elastic ear loops tested in this study had a mean (SD) FFE of 38.5% (11.2%) (Figure 3A), which was lower than that of medical surgical masks with tie strings (71.5% [5.5%]; n = 4). Tying the ear loops and tucking in the corners of the procedure mask to minimize gaps in the sides of the mask increased the mean (SD) FFE to 60.3% (11.1%) (Figure 3B). The “fix-the-mask” 3–rubber band modification and the nylon hosiery sleeve modifications, which were also intended to reduce gaps between the mask and the wearer’s face, improved mean (SD) FFE to 78.2% (3.3%) and 80.2% (3.1%), respectively.

    Modifications to improve the seal of the mask against the face by increasing the tension of the ear loops also improved FFE. Attaching the ear loops to the ear guards device using the center hooks (tightest option) increased procedure mask mean (SD) FFE to 61.7% (6.5%). Similarly, joining the ear loops behind the wearer’s head using a claw-style hair clip increased the procedure mask mean (SD) FFE to 64.8% (5.1%). None of the modifications tested enhanced procedure mask FFE to the level of an N95 respirator.

    Discussion

    In this study, consumer-grade masks and medical procedure mask modifications were tested as personal protective equipment (protection for the wearer) against a test aerosol of 0.05-μm NaCl particles. Although the FFE of consumer-grade masks and face coverings was variable, the FFE of some consumer-grade products exceeded that of medical-grade procedure masks. For example, the 2-layer woven nylon mask with ear loops was tested under various conditions, including with and without an aluminum nose bridge, with and without a commercially available nonwoven insert, and after 1 wash cycle in a standard household washing machine (air-dried on a drying rack). The unwashed nylon mask without a nose bridge or insert had an FFE of 44.7%. The addition of a nose bridge reduced visible gaps around the nose and increased FFE to 56.3%. Adding a nonwoven filter insert to the mask with the nose bridge in place resulted in a further increase in FFE to 74.4% (Figure 3C). Interestingly, the FFE of the nylon mask (with the nose bridge but without the filter insert) improved slightly to 79.0% after washing. It is unclear why washing alone improved the FFE from 56.3% to 79.0%. It may be that the washing/drying process unraveled some of the fibers to increase the overall filtration surface, and thus filtration efficiency, of the medium, or perhaps it modified the mask shape or size in a way that improved fit, or both. The washing/drying test was not repeated with additional nylon masks. Further investigation to assess the association of single and multiple washing with mask integrity and material disposition would be necessary to validate any improvement in FFE.

    The woven cotton mask, which comprises 3 layers and has a thin, flexible metal nose bridge, had the lowest FFE in this study (26.5%). The relatively loose weave of the cotton layers, while providing improved breathability and comfort, may reduce filtration efficiency. Additionally, we evaluated the FFE of improvised face coverings, including a standard cotton bandana and a neck gaiter balaclava bandana. The cotton bandana, when folded either bandit style or according to the US Surgeon General’s instructions, achieved approximately 50% FFE, which is better than the ear loop procedure mask we tested. Neck gaiter balaclava bandanas have also emerged as a popular face covering, particularly among athletes and young adults. As tested in this study, the single-layer gaiter, which was made of 92% polyester and 8% spandex and fits tightly to the wearer’s nose and mouth, had an FFE of 37.8%. While this face covering appeared to fit the wearer well, with no visible gaps in the seal, it may be that the relatively low FFE can be attributed to the low filtering efficiency of a single thin layer of woven material with large porosity.

    For medical procedure masks, modifications that enhanced the fit between the mask and the wearer’s face improved FFE. Simply tying the ear loops and tucking the corners of the mask against the wearer’s cheeks visibly improved mask fit and increased FFE from 38.5% to 60.3% (Figure 3, A and B). The most effective modification tested was the use of a nylon hosiery sleeve placed over the procedure mask. This modification, which held the mask tight to the wearer’s face, eliminated all visible gaps and increased FFE from 38.5% to 80.2%. However, donning the nylon sleeve over the procedure mask was cumbersome and limited the wearer’s ability to adjust the procedure mask. Generally, improvements in procedure mask FFE appeared to be associated with the integrity of the seal of the edges of the mask to the wearer’s face, demonstrating the importance of mask fit to maximizing filtration. While all of the modifications described in the Table enhanced protection against airborne particles for the wearer, not all were comfortable or practical for extended use. For example, the 3–rubber band “fix-the-mask” modification created considerable pressure on the wearer’s ears (visible in Figure 2E), making it uncomfortable after only minutes of wear and raising questions about its adoption by the general public. While the modifications shown in this article can improve mask fit and provide increased filtration of airborne particles, it is important to choose a modification in which discomfort is not a deterrent from wearing the mask for prolonged periods.

    Limitations

    The data presented in this article provide information on the use of masks and face coverings as personal protective equipment, which is defined in this study as protection for the wearer against exposure to an aerosol composed of small (0.05-μm) particles. However, we acknowledge that there are limitations to these findings. First, all FFE tests were performed on a single individual to ensure consistency and allow for a controlled comparison between test products. Interperson heterogeneity in facial geometries may result in variability of mask fit and differences in FFE. Second, the size of the NaCl particles used in this study (0.05 μm) may not reflect the most penetrating particle size for all of the mask materials tested. The most penetrating particle size for nonelectret filter media (filters that collect particles by aerodynamic rather than electrostatic mechanisms) can range from 0.2 μm to 0.5 μm.12 As a result, the reported FFE values at 0.05 μm may slightly overestimate the FFE of particles in the most penetrating size range. However, based on the mechanisms of particle deposition that govern filtration (ie, diffusion, impaction, interception, and sedimentation), it is clear that protection against aerosols of 0.05-μm particles would also confer similar or better protection against much larger aerosols or droplets,13 which are currently believed to be the predominant source for COVID-19 transmission.

    Conclusions

    Masks serve a dual purpose to protect the wearer and others. These analyses were designed to quantify the protection that masks offer to the wearer when exposed to others who may be infected. The exact FFE required to prevent respiratory virus transmission is not precisely known. However, evidence from previous studies suggests that even face masks with an FFE less than 95% (eg, surgical masks) are effective in preventing the acquisition of epidemic coronaviruses (SARS-CoV-1, SARS-CoV-2) by health care clinicians, except possibly during aerosol-generating procedures.6-8 For prevention of an associated coronavirus, SARS-CoV-1, N95 respirators had no increased prevention benefit over surgical masks.7 In this article, we reported that simple modifications to improve medical mask fit can substantially improve filtration efficiency. However, when FFE is considered (combined fit and material filtration), we demonstrated the practical effectiveness of consumer-grade masks to be, in many cases, nearly equivalent to or better than their nonrespirator medical mask counterparts.

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    Article Information

    Accepted for Publication: November 16, 2020.

    Published Online: December 10, 2020. doi:10.1001/jamainternmed.2020.8168

    Corresponding Author: Phillip W. Clapp, PhD, Department of Pediatrics, University of North Carolina at Chapel Hill, U.S. EPA Human Studies Facility, 104 Mason Farm Rd, Campus Box # 7310, Chapel Hill, NC 27599 (pwclapp@med.unc.edu).

    Author Contributions: Drs Clapp and Bennett had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Drs Clapp, Sickbert-Bennett, and Samet served as co–first authors and contributed equally to the work.

    Concept and design: Clapp, Sickbert-Bennett, Samet, Weber, Bennett.

    Acquisition, analysis, or interpretation of data: Clapp, Samet, Berntsen, Zeman, Anderson, Weber, Bennett.

    Drafting of the manuscript: Clapp, Sickbert-Bennett, Weber, Bennett.

    Critical revision of the manuscript for important intellectual content: All authors.

    Statistical analysis: Clapp.

    Obtained funding: Clapp, Sickbert-Bennett, Anderson, Weber.

    Administrative, technical, or material support: Sickbert-Bennett, Samet, Berntsen, Weber, Bennett.

    Supervision: Weber, Bennett.

    Conflict of Interest Disclosures: Dr Clapp reported grants from the US Centers for Disease Control and Prevention (CDC) and UNC/US Environmental Protection Agency (EPA) Cooperative Agreement during the conduct of the study. Dr Sickbert-Bennett reported grants from CDC Epicenter (U54CK000483) during the conduct of the study. Dr Anderson reported grants from CDC Epicenter (U54CK000483) during the conduct of the study; grants from Agency for Healthcare Research and Quality, personal fees from UpToDate, and royalties for authorship outside the submitted work; and being the owner of Infection Control Education for Major Sports, LLC. Dr Weber reported grants from CDC during the conduct of the study. Dr Bennett reported grants from CDC during the conduct of the study and grants from the National Institutes of Health, US Department of Defense, US Food and Drug Administration, Cystic Fibrosis Foundation, and EPA outside the submitted work. No other disclosures were reported.

    Funding/Support: This study was supported by the Duke-UNC Prevention Epicenter Program for Prevention of Healthcare-Associated Infections (U54CK000483) and a cooperative agreement between the University of North Carolina at Chapel Hill and the US Environmental Protection Agency (CR 83578501).

    Role of the Funder/Sponsor: The funding organizations had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

    CDC Epicenters Program Members: Phillip W. Clapp, PhD, University of North Carolina at Chapel Hill, Emily E. Sickbert-Bennett, PhD, MS, University of North Carolina Health Care, Deverick J. Anderson, MD, MPH, Duke University, David J. Weber, MD, MPH, University of North Carolina Health Care, and William D. Bennett, PhD, University of North Carolina at Chapel Hill.

    Disclaimer: The research described in this article has been reviewed by the Center for Environmental Public Health and Environmental Assessment, EPA, and approved for publication. The contents of this article should not be construed to represent agency policy nor does mention of trade names or commercial products constitute endorsement or recommendation for use.

    Additional Contributions: We thank Dr Bennett, the pictured author, for granting permission to publish this information.

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