At present, the masks that are certified to provide reliable protection against COVID-19 (minimum rating N95) are in short supply, so we have to buy or make our own untested mask. Here are some tips I have based on my years of work in environments that require respirators. The Center for Disease Control also offers guidance at its website (https://bit.ly/38gsyhE).
No exhalation valves. Half- or full-mask boatyard respirators often have an exhale valve because moisture in our breath deactivates the carbon used to protect against respiratory irritants (see Inside Practical Sailor, “Respirator and Dust Mask Safety”). For protecting others against COVID-19, an exhale valve is a big no-no, and the activated carbon filter is useless. Carbon should be replaced by an N95 filters, if you have them. Some N95 cloth masks also have valves. In both cases, you can cover the exhalation valve with piece of filter material, using tape or a rubber band to hold it in place.
Fit. Good fit is more important than the type of material you use. There should be no gaps at all. The bridge of the nose and under the chin are the most common leak areas. If your glasses fog, this means the fit is bad.
Most ear loop masks and pleated surgical-style masks will not pass a fit test. They seldom fit right and they are generally too loose. You can modify them to tie or wrap around your head for better fit—or look for another style.
Duckbill style. The internet is full of do-it-yourself designs that you can make in a pinch. In my observations, the only DIY type that is easy to use and reliably fits is the duckbill style. With a horizontal seam, these look a little sillier than the vertical seam masks, but I’ve found they fit better. The pattern is here (https://bit.ly/2BcRyu7).
There are YouTube videos that show how to make one, like this one from an emergency room doctor (https://bit.ly/31w2eP0). He suggests using a HEPA vacuum cleaner bag. This design probably does meet the N95 requirements, although the bag manufacturers do not stand behind this claim. You can sew the same mask from multiple layers of fabric and probably get equivalent filtration. Multiple layers are good, with at least one layer of fine cotton sheeting. In general two layers of fine cotton sheeting should perform as well as N95 fabrics.
Disinfection. You can avoid cross-contamination by learning to don and doff the mask without touching your face. Always sanitize hands before and after handling. A cloth mask can be washed or sanitized, but avoid chemicals or excessive heat that can damage the filtration or fit. We drop our cloth masks in a soapy solution, let them soak, rinse, and then let them dry in the sun. You can also use steam or dry heat—depending on the material. Guidelines for reusing masks are at the CDC website (https://bit.ly/2NHZ1nA).
Finally, masks are not a cure-all. A mask can leak. You could put it on wrong or touch your face with contaminated hands if you are not careful. Don’t get a false sense of security. Continue to give people some distance and practice careful sanitation. For more details on the latest developments in the fight against COVID-19, Belvoir Media has teamed up with Harvard Medical Center to create the Coronavirus Resource Center: https://www.health.harvard.edu/diseases-and-conditions/coronavirus-resource-center