Filters add an extra layer of protection against the virus and make your homemade mask more effective.

By Jessica Bennett
April 24, 2020
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By now, we all know to wear some type of cloth face mask when outdoors to help prevent the spread of coronavirus (the masks block potentially virus-causing droplets that are released into the air when a person coughs, sneezes, talks, or even breathes). However, you might not know that adding a filter to your homemade mask can make it even more effective. Filters are especially important if your mask is made of thin or loosely woven fabric, like those used for scarves and T-shirts, which might not offer enough protection against the virus. In fact, a study from Missouri University of Science and Technology found that masks made from a bandana with no filter only blocked about 10-20% particles, compared to an N95 mask that blocks more than 90%.

Credit: Rike/Getty Images

4 Items You Can Use as a Face Mask Filter

The good news is you can make a good filter from a variety of household materials. After cutting the material to size, it's best to place the filter between layers of fabric, as some materials might shed small fibers that could be harmful to inhale. You can tuck the filter between folds of fabric or create a pocket inside the mask to hold it in place. Make sure the filter is easily removable so you can replace it after each use.

1. HEPA Filters

Typically used in furnaces, air conditioners, and some air purifiers, multi-layered HEPA (which stands for high-efficiency particulate air) filters are nearly as effective as N95 masks at blocking aerosols, according to research from Missouri University of Science and Technology.

2. Paper Towels

Although not entirely effective as a mask material by itself, a paper towel can be used as a filter inside fabric face masks. A double layer of paper towels can increase virus-blocking capability by 33%, research from air purifier company Smart Air shows.

3. Coffee Filters

Coffee filters were also found to be highly effective at capturing particles, but low breathability might be an issue for face masks. However, some bagged coffee filters might allow enough airflow to be used as a homemade mask filter.

4. Nylon Stockings

Apart from placing a filter inside the mask, another option is to add an additional layer of filtration on top. A recent study from Northeastern University found that layering a nylon stocking over a face mask can make it up to 50% more effective at blocking airborne particles. By creating a tighter seal around the face, the nylon layer helps ensure particles can't slip in around loose edges of the mask.

Must-Know Tips to Boost Your Face Mask's Safety

It's important your homemade face mask filter allows for airflow. If not, the particles can go around the filter instead of through it. To test a filter's breathability, hold the material tightly against your face to make sure you can breathe through it before using it for a face mask.

Next, make sure your mask fits properly around your face. If you don't have access to a filter, you can maximize protection by opting for a design with multiple layers of fabric. In general, fabrics with a tighter weave, such as quilter's cotton fabric or high-thread-count bed sheets, are more effective at blocking particles. To check a fabric's effectiveness, hold the material up to a light. If light shines through, you might want to choose a more tightly woven fabric.

If you do decide to add a filter to your homemade mask, remember to remove and discard the filter after wearing it in public and wash your face mask frequently. Regardless of what your mask is made of, some protection is better than nothing, but practicing social distancing remains your most effective line of defense against coronavirus.

Comments (5)

Anonymous
May 23, 2020
Dear Anonymous: You remove and throw away the paper towel before you wash the mask.
Anonymous
May 18, 2020
HEPA Filters are NOT recommended for face masks! Most HEPA filters contain fiberglass which can cause serious respiratory irritation or damage if inhaled.
Anonymous
May 17, 2020
You make a pocket to be able to remove the filters.
Anonymous
May 15, 2020
I would be very cautious about advising people to use furnace filters as face masks. Some contain fiberglass whose tiny fibers are released when cut. Fiberglass should never be inhaled. While vacuum bags do not contain fiberglass, some manufacturers, such as Shop-Vac, have expressly warned against using their bags for unintended purposes. In short, those products were never meant to be used as face masks for people. Therefore, their safety has never been tested for such use.
Anonymous
May 14, 2020
If you put a paper filling in your cloth mask, how are you supposed to wash it?