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Author: Jeffrey W. Herrmann, Professor, Department of Mechanical Engineering and Institute for Systems Research, University of Maryland.
During the coronavirus pandemic, face masks have become an important tool for preventing transmission of the virus and protecting health-care workers, but commercial face mask supplies are low. Members of the public are mobilizing to make face masks, but there are many different designs and options that have different purposes. This web page is based on information from various health care organizations (see Links at the end of this page). It provides a systematic way to decide which face mask someone should make.
Many of the options listed here were reported by Sindya Bhanoo in The Washington Post, April 3, 2020.
Purpose: First, different types of face masks have different purposes:
Materials: Some masks should be made from cloth, but others are made from paper. Some materials may be difficult or impossible to obtain. Using material that you already have will be easiest. Different materials perform differently; see Material Performance below.
Assembly: Some masks require cutting and sewing together multiple pieces of fabric and other techniques; some masks can be made with scissors and tape. If the masks are for a health care provider, consider these guidelines for sanitary assembly.
Masks to prevent infections: These masks are being considered by hospitals as substitutes when their supplies of regular masks are gone. Some hospitals are accepting donations of such masks; check with your local medical providers These masks should be useful to protect oneself as well.
Each mask in the list gives the organization who published the mask, the key materials, the ease of assembly, and links to instructions.
Masks to protect N95 and surgical masks: These masks keep valuable N95 and surgical masks clean so that they can be used for a longer period of time, which reduces demand. Light-colored fabrics are best; they it make it easy to determine when the mask is soiled. For some designs, using different fabrics on the different sides is useful. These masks were suggested by OSCMS.
Masks to prevent the spread of coronavirus: These masks stop the droplet emitted by someone who is infected, even if the infected person is showing no symptoms, which prevents the person wearing the mask from spreading the virus. There is no evidence that such masks protect the persons wearing them (because one gets the virus by touching an infected surface and then touching their face). As of April 3, 2020, the CDC recommends "wearing cloth face coverings in public settings where other social distancing measures are difficult to maintain."
Many face mask patterns call for tightly-woven cotton cloth. Others use paper towels and facial tissues. One doctor has recommended Halyard H600 two-ply spun polypropylene, a sterile wrapping that is normally used to surround surgical instrument trays before they pass through gas sterilization or an autoclave (University of Florida Health).
Two key attributes of materials for face masks are filtration efficiency and breathability. The following chart is based on data from the Open-Source COVID-19 Medical Supplies (OSCMS) community. Greater filtration efficiency and breathability are better. (Author's note: I'm not sure how the breathability of a vacuum cleaner bag can be 140% lower than the breathability of a surgical mask; please see the OSCMS document for more information.)
Last updated on April 10, 2020, by Jeffrey W. Herrmann.