ConsumerLab.com Answers
How to Make or Buy an Effective Mask
Reviewed and edited by Tod Cooperman, M.D. Tod Cooperman, M.D.
Initial Posting: 5/5/2020 Last Update: 8/15/2020
Question:
How can I make a mask that is as good as a surgical mask or an N-95 mask?
Making a Homemade Mask as Effective as Surgical and N-95 Mask -- Cloth Masks, Scissors and Fabric
Answer:
If made with the right household materials, you can create a mask that may be as effective as a medical mask and, in some ways, similar in blocking efficiency to an N-95 respirator (although not a replacement for an N-95), according to several laboratory studies. Masks can be used alone or, for increased protection, particularly for the eyes, with a face shield.
Below we discuss the details of masks and how to make them. We also identify what seem to be best disposable filter materials.
If you would prefer to buy a mask, we have identified several brands that appear to meet the specifications of the World Health Organization (see Best cloth masks you can buy).
Why you should wear a mask -- and why it should be an efficient one
Along with social distancing, a mask provides additional protection from infecting others as well as preventing exposure. A review of studies found that transmission of SARS-CoV-2 and related coronaviruses was 82% lower with physical distancing of 1 meter (3.3 feet) or more, compared with shorter distances, and protection might increase with additional distance. Face mask use could result in an 85% reduction in risk of infection versus no face mask, with stronger associations for N-95 or similar respirators, while surgical masks and multi-layered cotton masks were less effective but offered more protection than single-layer masks (Chu, Lancet 2020).
An analysis of rates of growth of COVID-19 infection in U.S. states found that the mandated use of masks in public issued by 15 states in April and May, 2020 was associated with a decline of about 1% in the daily COVID-19 growth rate within the first week of the mandates and a 2% decline 21+ days after mandates were issued. Although the effect is modest, the researchers estimated that by May 22, 2020, 230,000 to 450,000 COVID-19 cases may have been averted due to the mandates (Lyu, Health Aff 2020).
Any benefit to wearing masks at home?
Although CDC guidelines do not currently include the use of face masks at home, the rate of transmission from one household family member to another was 79% lower when members wore face masks prior to the first member developing COVID-19 symptoms, according to a study of 124 families in Beijing in which there was at least one infected person. Overall, there was a 23% rate of transmission of COVID-19 from an infected family member to another, but this was no lower when mask wearing began after the first member developed symptoms. These results are consistent with the fact that viral load is highest two days before symptoms and on the first day of symptoms. Daily use of disinfectants reduced transmission by 77%. Transmission rates were four times higher if the primary case had diarrhea and 18 times higher when there was frequent daily close contact (less than 3 feet apart). The researchers recommended use of face masks in families in which a member has been at risk of getting infected. In China, over 70% of transmission occurred within families (Wang, BMJ Global Health 2020).
Best combination of materials for making a mask
The World Health Organization (WHO) recommends using three layers of fabric for non-medical, cloth masks in order to achieve the best combination of filtration efficacy and breathability:
1. Innermost layer: Hydrophilic material (i.e., one that can absorb moisture, such as cotton or cotton blends)
2. Middle layer: Hydrophobic material (i.e., repels moisture) of synthetic non-woven material such as polypropylene or a second cotton layer which may enhance filtration or retain droplets.
3. Outermost layer: Hydrophobic material (e.g., polypropylene, polyester, or their blends) which may limit external contamination from penetration through to the wearer's nose and mouth.
(See Best cloth masks that you can buy for our review of masks for sale that appear to meet the WHO requirements)
Note that polypropylene, a material often used to make disposable surgical masks, has an electrostatic charge which can improve the filtration efficiency of masks. Polypropylene "spunbound" is sold in fabric and many other retail and online stores under brand names such as Oly*fun and Pellon. Polypropylene is sold in different weights (measured in grams per square meter or GSM). Most commercially manufactured surgical masks are made of 3-ply 25GSM. Polypropylene materials between 25 and 40 GSM tend to have similar filtration efficacy and breathability, while polypropylene 60 GSM has a higher filtration efficiency but less breathability (Zhao, Nano Lett 2020). Be aware that some forms of polypropylene should not be machine washed.
See below for a more detailed discussion of the filtration efficacy of various cotton and synthetic household fabrics.
How cotton and other household fabrics compare in blocking coronavirus
The first study, from the University of Illinois at Urbana-Champaign, found that many household fabrics can be as effective as the material in surgical masks for blocking droplets of sizes known to carry the COVID-19 (SARS-CoV-2) coronavirus. The blocking efficiency of a commercial medical mask was found to be 96.3%, while the blocking efficiency of a used dish cloth (85% polyester and 15% nylon) was slightly better -- 97.9%. In addition, most household fabrics were more breathable than the material in a medical mask. The dish cloth, for example, was twice as breathable as the medical mask (Aydin, medRxiv 2020 --preprint). (See the CDC website to learn how to make a cloth face covering.)
A study at the University of Chicago and Argonne National Laboratory found that tightly woven, high-thread count cotton (600 thread-per-inch (TPI) sheet by Wamsutta) was more effective in filtering large droplets (similar to larger-sized SARS-CoV-2 droplets) than loosely woven cotton with a lower thread count (quilters cotton, 80 TPI), while fabrics with an electrostatic charge (such as silk and chiffon) were best for blocking aerosols -- the smaller sized droplets that remain suspended in air for extended amounts of time. Using layers of both fabrics, together, was most effective for blocking both large and small droplets. For example, two layers of 600 TPI cotton fabric had a large particle and small particle blocking efficacy of 99.5% and 82%, respectively, but one layer of 600 TPI cotton combined with two layers of chiffon (90% polyester, 10% spandex from Jo-Ann Stores) had a large particle and small particle blocking efficacy of 99.2% and 97% -- which, at low airflow rates (i.e., when not all air is drawn through the mask) is nearly as good as a properly-fitted N95 mask for blocking large particles and better than the N-95 with respect to small particles, of which only 85% are blocked by an N-95 mask). However, as emphasized in a published correction to the study, it is not known how efficient this fabric combination will be at normal or high rates of airflow when made into a fitted mask, i.e., when there are no leaks and all air flows directly through the mask, particularly when one is engaged in high levels of exertion. The researchers also found that small holes or leaks around the edges of the fabrics could decrease the blocking efficacy by 50% or more, and emphasized the importance of a good fit (snug and without gaps) (Konda, ACS Nano 2020). [Note: An illustration in the study shows the electrostatic layer of fabric as the inner layer when fabrics were combined. However, ConsumerLab contacted the author of the study who suggested that electrostatic fabric (such as chiffon) may be best used as the outer layer of the mask to avoid humidity from the nose or mouth, which could interfere with the electrostatic properties, but emphasized that was his suggestion, not something that was tested in the study.]
In another study, researchers at Florida Atlantic University tested masks made from common household fabrics, as well a typical "cone" mask (often sold at pharmacies) to see how well they worked to stop droplets using a simulated model of coughing (a mannequin head through which liquid was manually pumped). Without any covering, droplets from the simulated cough traveled an average of 8 feet. With a bandana (single-layer, elastic T-shirt material, 85 threads per inch) droplets traveled an average of 3 ft. 7 inches, with a folded cotton handkerchief (as shown in this instructional video featuring the U.S. Surgeon General), 1 ft. 3 inches, and with a cone mask (CVS Cone Face Mask), 8 inches. The most effective mask was a stitched cotton mask (using two-layers of cotton quilting fabric, 70 threads per inch), with which droplets traveled just 2.5 inches. The researchers noted that "healthcare professionals trained properly in the use of high-quality fitted masks will not experience leakage to the extent that we have observed in this study. However, leakage remains a likely issue for members of the general public who often rely on loose-fitting homemade masks." (Verma, Physics of Fluids 2020).
Rather than focus on how far droplets travel, researchers at Duke looked at how well different masks block droplets during speaking. A fitted N95 mask without a valve was most effective in retaining droplets, with less than 1% of droplets being transmitted. The next most effective, in order, were a 3-layer surgical mask, a cotton-polypropylene-cotton "apron" mask, a 2-layer polypropylene mask, a 2-layer cotton pleated mask, and then an N95 with a valve. Two masks offered little protection: A double-layer bandana was only slightly more effective than using no face covering at all, while the worst face covering was a "gaiter" style neck fleece (often worn during running or sports) that showed a 10% increase in the number of droplets. The researchers suggested that the neck fleece material breaks larger liquid droplets into smaller droplets than can more easily be dispersed into the air (Fischer, Sci Adv 2020 — includes photos of the masks but no details about origin or brands).
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