Now that the Centers for Disease Control and Prevention (CDC) is encouraging everyone to cover their mouth and nose with a protective cloth face mask, people are making their own to protect against COVID-19, whether they’re no-sew, made with a simple bandana, made of a T-shirt or sewn on a machine.
And as more and more brands sell face masks that claim to be effective against the coronavirus, it’s important that you understand whether the materials they’re made of are actually helpful.
A study of homemade face masks by SmartAirFilters.com found that cotton T-shirts and cotton pillowcases are the best materials for making DIY face masks, based on their ability to capture particles yet remain breathable, and that they perform comparably to surgical-grade masks.
But some people opt to add an additional filter inside their masks as an extra protective layer to mimic the powerful N95 masks used in hospital settings. DIY masks made with HEPA vacuum bag filters and coffee filters are already beginning to gain popularity on Pinterest. And chances are, you’ve probably seen them on Instagram, too.
But which are the best materials to use? We tapped two medical professionals and a COVID-19 survivor who makes mask patterns online to give you the lowdown on the best filter fabrics to use when crafting a mask of your own.
What does a filter do?
Although cotton tea towels and pillowcases can make effective face masks, research is suggesting that filters can be equally important.
For example, Yang Wang, assistant professor of environmental engineering at Missouri University of Science and Technology, told The New York Times this week that the use of filters helps promote safe breathing and ensures that particles are removed properly.
However, Stanford physician Sudeb C. Dalai told HuffPost that the placement of your filter (which you should replace often) is very important. Filters must be sandwiched between two layers of fabric to prevent the inhalation of filter materials.
“It should be noted that any filter material (HEPA, polypropylene) should be sandwiched in between two additional layers of fabric (cotton, silk or nylon) to prevent inhalation of filter materials, and protect the face from the abrasive material,” he said.
Dalai added that you’ll want to ensure that your filter fabric does not extrude high amounts of fiber and other synthetic materials since the inhalation of glass fiber can cause respiratory diseases in humans.
“It is important to choose a fabric that allows clear, unobstructed breathing, does not saturate easily with moisture and does not extrude high amounts of fiber or other synthetic materials that could be inhaled,” he explained.
Do HEPA vacuum filters work?
When it comes to selecting an effective mask filter, Dalai said that HEPA-certified vacuum filters are among the best household items to use.
“HEPA vacuum filters have a high efficiency for filtering very small particles, including the microscopic droplets responsible or the majority of respiratory virus transmission,” he told HuffPost. “These filters are breathable, are easy to obtain and do not extrude large amounts of inhalable synthetic materials.”
But if you don’t have a vacuum filter at your disposal, DIY face mask pro Juliana Sohn told HuffPost that HEPA vacuum bags can also be included in your mask. Sohn, a COVID-19 survivor who has been actively sharing mask patterns on Instagram, recommended ensuring your vacuum bag is made without dangerous materials such as fiberglass.
“The gold standard for filters made of household items for your homemade mask are HEPA vacuum bags,” she said. “You have to make sure they are made of polypropylene, and not with fiberglass.”
Sohn also suggested the use of air conditioner filters. However, like vacuum bags and filters, it’s important to avoid products that have fiberglass materials.
“People are also starting to order air conditioner filters,” she added. “Again, it’s always important to make sure it’s not made with fiberglass.”
What about non-woven polypropylene material?
Polypropylene non-woven fibers (used in non-shiny reusable fabric grocery bags, tote bags and wine bags) also make adequate filter fabrics.
“This is the same material used in N95 masks, although the thickness and weave are different,” Dalai said.
But in addition to thickness, Sohn said that grocery store tote bags made with non-woven polypropylene have the advantage of being easily laundered, allowing you to use them again and again.
Coffee filters, paper towels and tissues are less effective.
Although new CDC instructions for making DIY face masks include incorporating a coffee filter, board-certified internist Nate Favini said that coffee filters, paper towels and tissues (even in layers) aren’t very effective at filtering out microscopic particles. And they can’t be washed.
However, that doesn’t mean you can’t use them, especially if they are the only materials you have at your disposal.
“It is probably still a good idea to use these as filters if you don’t have another choice available to you,” he told HuffPost. “The CDC instructions for making a mask include an option that incorporates a coffee filter.”
Aside from poor filtration properties, Dalai said that coffee filters can become easily saturated with moisture. So masks made with these paper materials are suitable for one-time use only.
Are filters essential?
Although the CDC recently changed its guidance to encourage the public to use DIY face masks made from protective cloth, Favini said that there is no requirement to put in filters at this time.
However, because anyone could be an asymptomatic carrier, he told HuffPost that any filtration and coverage (along with adhering to social distancing guidelines, of course) is better than nothing.
“Because anyone could be an asymptomatic carrier, there is no harm in wearing a mask,” he added. “As long as it is homemade, and is not a medical mask (which should be reserved for health care professionals), you should be fine.”
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