The CDC now recommends that everyone wear a fabric face mask when out in public (https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/diy-cloth-face-coverings.html). This is more to protect others if you have been exposed and don’t know it yet, but anything is better than nothing when it comes to reducing your chances of breathing in a droplet with viral particles inside. For the love of our medical professional heros, please don’t use a medical-grade mask unless you have one lying around already. Let’s save all of the more protective equipment for people who are at highest risk because they are taking care of lots of very sick people.
Some handmade masks are better than others when it comes to protection, though. Ideally you want a tight fit so that you are breathing through the fabric rather than having air come in on the sides of the mask. Consequently it has to be breathable, or else the air will mostly route in through the sides. You also want tightly woven fabric if possible, because knit fabric has lots of large holes that air can pass through. One good way to see how permeable your fabric might be is to hold it up to a light and see how much light you can see through the fabric (https://www.nbcnews.com/health/health-news/making-your-own-face-mask-some-fabrics-work-better-others-n1175966). If you have a choice, go with the fabric that blocks the most light but is still breathable. However, you can make up for more porous fabric by using a mask design that incorporates a filter, or by using multiple layers of fabric in your mask.
You also need to be careful how you use a fabric mask. Take it off when you come home, and don’t touch the outside of the mask when you take it off. Wash your hands after taking off the mask, especially if you accidentally touch the outside. Wash it after each use in hot water.
Ultimately, though, all of the optimization advice in the world doesn’t help if you are limited by what you have on hand. Something is better than nothing, even if you are tying on a bandana. The outside of the masks I am making for my family is fabric from an old pair of my spouse’s shorts (see above picture). It blocks the light well and is breathable, but I don’t want to make strangers breathe through used shorts fabric.
Probably the best option- Sew a tight fitting mask like this one: https://twin-cities.umn.edu/news-events/diy-face-masks-during-covid-19
However, there are easier ones to make that are also faster to mass produce if you are donating masks, like this one: https://www.sewgoodgoods.org/face-mask-covid-19
There are also ways to make a mask with a piece of material and rubber bands. This is a video of Surgeon General Jerome Adams making a mask very quickly from materials that almost everyone has at home: https://www.youtube.com/watch?v=tPx1yqvJgf4
In a pinch, even the CDC agrees that if you have a bandana it is still better than nothing.
I wanted to take a minute here at the end to talk about something that has disturbed me greatly. African Americans have been kicked out of stores for wearing masks (https://www.washingtonpost.com/business/2020/04/09/masks-racial-profiling-walmart-coronavirus/), which is insane. People of color also worry that they might be increasingly racially profiled if they wear masks (https://www.nbcnews.com/news/nbcblk/black-men-fear-homemade-masks-could-exacerbate-racial-profiling-n1179236). This makes everyone less safe!! African Americans in particular have shown higher death rates from COVID-19 (https://www.nbcnews.com/news/nbcblk/african-americans-may-be-dying-covid-19-higher-rate-better-n1178011), so we need to protect them by helping reduce their risk of getting sick. We need to both make sure everyone has access to fabric masks, and not look with suspicion upon people wearing masks.
When you see anyone wearing a mask, please thank them from a safe distance for doing their part to protect everyone!