N95Decon Research Document. Not Peer Reviewed.
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Technical Document for Public Useof Medical Masks and Cloth Masks
Executive Summary

During the COVID-19 pandemic, universal mask-wearing in public protects others and will
provide some protection to the wearer. Face masks are used across the world to reduce thetransmission of respiratory viruses.
Masks protect the greater community and protect the individual from infection:
1) For people near the wearer: When covering both the nose and mouth, masks can
reduce emission of virus-containing respiratory droplets and aerosols from people whohave been infected. SARS-CoV-2 (the virus that causes COVID-19) can be transmitted
from people who do not have symptoms or do not feel sick, so face-mask wearing is
now widely recommended or mandatory in public.
2) For the wearer: Data support that masks reduce the number of viral particles that arebreathed in through the mouth and nose. For the inhaled air to be effectively filtered, thetype of mask and how it is worn are critical.
This document reviews basic features of masks that create a droplet barrier and are correlatedwith higher filtration of inhaled air, to provide protection from viral transmission. In most cases,
any mask or face covering is better than nothing at all. However, the level of protection
provided to the wearer, and others, varies depending on several variables including the type ofmask and how it is worn.

1. Overview

The Centers for Disease Control and Prevention (CDC) recommends the use of facemasks to reduce transmission of COVID-19 in public, especially in areas where significant
community transmission may occur, such as grocery stores and pharmacies (CDC, 2020). In
combination with maintaining a 6 ft. distance from other people, wearing a face mask further
reduces risk of transmission. Albeit only a correlative connection, in countries wheretransmission has been effectively mitigated (e.g. Taiwan, Hong Kong, Korea, and parts ofChina outside of Hubei), face mask use has been widely practiced in public from an early stage
in the pandemic (e.g. National Health Commission of the People’s Republic of China, 2020).
Here, we briefly describe the differences in protection from COVID-19 that are provided
by N95 filtering facepiece respirators (FFRs), medical masks (also referred to as surgical orprocedure masks), and cloth masks. N95 FFRs provide the highest protection from being
infected but, due to the supply chain shortage, the CDC recommends that these be reservedfor health care workers. For health care workers, we have provided detailed information about
N95 FFRs on other www.n95decon.org pages. Here, we review data on the features of medical
masks and cloth masks that reduce viral transmission from a sick person or provide protection
from breathing in of viral particles by a well person. Given the wide variety of medical and clothmasks available, we can only provide a broad comparison here.

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2. For Protection, Masks Must Cover the Nose and Mouth

SARS-CoV-2 virus is found in the nose mucus, saliva, and feces of infected individuals(Singhal, 2020). SARS-CoV-2 infects new hosts by entering the body through the nose, mouthand eyes (Tu et al., 2020). Infection can occur either directly by transmission through the air orby transmitting viral particles from a contaminated surface to the face, for example by handface contact. People touch their faces frequently, especially mucous membranes (Nicas &Best, 2008). Reducing hand-face contact can reduce viral transmission by protecting an
individual in a setting where surfaces or items may be contaminated and their hands frequently
touch those surfaces or items, such as a hospital, grocery store, post office, etc. Therefore, formaximum protection while wearing a mask, it is important to avoid touching the face in order toadjust the mask. When putting on, wearing, and removing the mask, the wearer should nottouch the exterior or interior of the mask and instead handle it only by the earloops, to reduce
the risk of contaminating it. Wash hands before putting the mask on and after taking it off.

3. Masks Reduce Virus Transmission From the Mask-Wearer

When infected people cough, sing, sneeze, blow their nose, speak and exhale,
respiratory droplets (or mucus) are expelled. When an infected person wears a mask over theirnose and mouth, expelled virus-containing respiratory droplets and aerosols are partially
blocked (Leung et al., 2020). Respiratory droplets project particularly far when we are
speaking, singing or coughing, as shown in a video with Dr.Harold Varmus, Nobel laureate, andformer head of the National Institutes of Health (Stop COVID-19, 2020). Moreover, it has beenshown that samples of room air and circulated air can contain SARS-CoV-2 (Liu et al., 2020; Lu
et al., 2020; Ong et al., 2020). SARS-CoV-2 aerosols can remain airborne for 30 min–3 hrs,
depending on the size of the particles and conditions such as humidity and ventilation (vanDoremalen et al., 2020). Thus, even if people are staying 6 ft. apart, they might share breathspace in less time than it takes the droplets to fall to the ground. While social distancing to atleast 6 ft. is a key line of defense, proper mask use directly impedes transmission by reducing
the number of virus particles that are released into the air.
Importantly, COVID-19-positive individuals can be infectious during the initial days ofinfection, when symptoms are mildest or not present (Kimball et al., 2020; Rothe et al., 2020;
Wei et al., 2020; Zou et al., 2020).Thus, even people who feel well should wear a mask tominimize respiratory droplet emission in public. Such precautions would be expected to reducetransmission such as occurred in the tragic case of a 60-person choral group in Washington. In
this case, although people reported that no one was coughing or feeling ill and there was very
little direct contact, shortly after the choral practice most of the members became ill, 28 wereconfirmed positive for COVID-19, several were hospitalized, and two members died (Waldrop
et al., 2020).

4. Masks Reduce Virus Inhalation by the Mask-Wearer
Medical and cloth masks not only reduce respiratory droplet transmission to the outsidefrom the wearer (Leung et al., 2020), but also reduce the number of particles that reach theinside of the mask from the outside, thereby protecting the wearer (van der Sande et al., 2008).
One carefully controlled study (Lai et al., 2012) was done with mannequins, where one expelled
respiratory-like particles at 1 or 2 feet from another mannequin that wore either a fully-sealed

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mask (e.g. N95 FFR) or a mask with gaps under the eyes or on the sides (e.g. a medical-typemask). The number of particles ‘inhaled’ by the masked mannequin was measured to assess
protection. The fully-sealed mask provided >97% protection under all conditions, including a
mimicked cough at a short distance. The medical mask provided between 30% and 100%
protection, depending on the number of gaps between the mask and the face, for how long theother mannequin was expelling particles, and the distance from the other mannequin. Anotherstudy with mannequins used influenza viral particles and found that medical masks blocked >50% of infectious viral particles that were breathed in (Noti et al., 2012). These data support
that maintaining social distancing is a key protective factor but that mask wearing provides
additional protection. Thus, mask-wearing is especially important to protect frontline service
workers who must interact at <6 feet from others.

5. Difference Between N95 FFR and Medical Mask

Here, we discuss a broad mask category known as “procedure”, “medical” or “surgical”
masks. These masks are different from the N95 FFR. N95 FFRs block at least 95 percent ofvery small (0.3 μm) test particles because they form a complete seal on the face, forcing all of
the breathed air to go through filtration.
Medical masks differ from N95 FFRs in a number of ways. Most importantly, medical
masks do not seal to the face. They are fabricated from flexible material containing a filter thatis thinner than that of the N95 FFR, and they are meant to be open at the back edges forbreath to escape, rather than the complete seal provided by the N95 FFR. Medical masks are
manufactured with various filtering capabilities and hence come in different grades. Medical
masks, when at quality standards, are 3-ply, with a water resistant outer layer and a middle
layer composed of electret material such as polyethene or melt-blown polypropylene that issimilar to that of the N95 FFR, but not as thick. Electret-based filters are a type of material thattraps respiratory droplets and other particles by electrostatic charge attraction and therefore
can have a relatively large pore size for good airflow/breathability (Martin & Moyer, 2000).
Electret filters make the medical masks and N95 FFRs generally more effective than clothmasks.
The ability of a medical mask (or cloth mask) to filter particles critically depends
on the proportion of air that passes through the filter rather than through gaps aroundthe mask, which is not filtered at all. Therefore, reducing the number and size of gaps byadjusting a medical mask to fit closely to the wearer’s face will enhance its protective function(Konda et al., 2020; Mueller & Fernandez, 2020).

6. Comparison of Medical Masks and Cloth Masks

Because electret materials are not readily available to the public, cloth masks rarely
have the same combined features of high filtration and high breathability as medical masks(Martin & Moyer, 2000; Davies et al., 2013). A major challenge for cloth masks is therefore tofind a material that has high filtration, but also high airflow so that the air breathed comes tothe wearer through the filter, rather than via gaps in the sides. The fiber pattern of woven
fabrics generally provides higher filtration when in multiple layers or tighter weaves (higher
threads per inch). However, the material properties (e.g. charge) also affect filtration efficiency(Martin & Moyer, 2000; Konda et al., 2020).
Commonly available materials with the best filtering efficiency are amorphous, bonded
materials such as paper towels, shop towels or vacuum cleaner bags however, these materials

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often have low airflow (Davies et al., 2013). Moreover, these materials may contain respiratory
hazards such as carcinogenic compounds found in vacuum cleaner bags (Mueller &Fernandez, 2020). Another benefit of medical masks is that they have a hydrophobic outerlayer that blocks liquid penetration, a feature not common to home-made masks.
Quality medical masks are designed to have a bendable nose-bridge to minimize thegap below the eyes, and gathered material on the sides to form a gap where exhaled air canescape toward the back, away from the person in front. Cloth masks with this pattern of few
gaps should be more effective. By contrast, bandanas typically have gaps below the eyes andalso a gap below the mouth, which could lead to a virus-infected person’s breath going down
to their workspace. In conclusion, existing data suggest that medical masks are more effectiveat protecting the wearer and the public than cloth masks are (van der Sande et al., 2008;
Davies et al., 2013; Mueller & Fernandez, 2020) but, with proper design, cloth masks can also
be highly effective at limiting viral transmission to the public (Davies et al., 2013; Mueller &Fernandez, 2020; Konda et al., 2020). Wearing a mask, therefore, has a clear benefit for
infection control, irrespective of whether the mask is cloth or medical. For a more detailed
treatment of this topic, refer to the National Academies Rapid Expert consultation on theeffectiveness of fabric masks for the COVID-19 pandemic (National Academies of Sciences &Medicine, 2020).
In conclusion, the available data support implementing both social distanding and useof medical masks. This protects infected people from spreading the virus and susceptible
people from becoming infected. Computational modeling, not yet peer-reviewed (Worby &Chang, 2020), suggests that mask use will reduce deaths from COVID-19, especially whenused by the vulnerable elderly population and by people who are sick.

7. Decontamination of Medical and Cloth Masks

The CDC recommends frequent washing of cloth masks because soap and hot water
should suffice to decontaminate cloth from SARS-CoV-2. Medical masks cannot be washedbecause soap and agitation will reduce hydrophobicity and the ability of the electret to filter
particles, rendering them less effective. Like N95 FFRs, medical masks are indicated for one
time use (CDC, 2020). SARS-CoV-2 can survive for days on various materials (Doremalen et al.,2020). On surgical masks it was found that one week after application of a large dose of SARSCoV-2 there was virus remaining (Chin et al., 2020). The exact time needed for a more typicaldose of viral contamination to degrade is unknown but will be sensitive to temperature,humidity, and material of the medical mask. More data is needed for a precise
recommendation. If a medical mask must be reused, it should be reused only by its originaluser, after being stored for more than a week in an isolated, clean, and aerated location.
Potentially contaminated materials should not be brought home, as this carries significant
contamination risk.
The Content provided by N95DECON is for INFORMATIONAL PURPOSES ONLY, DOESNOT CONSTITUTE THE PROVIDING OF MEDICAL ADVICE and IS NOT INTENDED TO BE
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SOLELY AT YOUR OWN RISK. A link to the full N95DECON disclaimer can be found athttps://www.n95decon.org/disclaimer

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