Which Filters You Should (& Should Not) Use In Your Protective Face Mask

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Do We Need Filters For Homemade Or Fabric Masks? Which Filters Work Best To Protect You

As we continue to wear masks while leaving home, which is quickly becoming a worldwide standard, people are looking for ways to not only make their masks more comfortable and wearable, but also more effective in filtering out germs.

Though there are a few different types of masks, do we need filters for our homemade or fabric/cotton masks?

Depending on the materials used in face masks, a filter isn't a requirement, but it could be very helpful.

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A filter is used to add extra protection both to the wearer and to the people around them. If you use cotton material that isn't threaded tightly enough, some germs and particles in the air will get through — both going out and in. With a filter, that risk is reduced.

According to a study from Wake Forest Institute for Regenerative Medicine in North Carolina, the efficacy of homemade masks can vary substantially based on the material it’s constructed with.

Says Keane Veran, co-founder and CEO of OURA, a company that manufactures reusable antimicrobial medical-grade masks, “As necessary as filters should be in a homemade mask, by adding a filter, there's a trade-off between breathability and filtration. There are several studies that back having additional layers of fabric (or filters) to improve the efficiency in which particles are filtered."

To help us breathe easier while wearing a mask, what types of filters should we avoid?

1. HEPA filters

Some HEPA filters and vacuum bags are made with fiberglass that tear away from the filter through continued use. 

Warns Veran, “I strongly recommend against HEPA filters. Inhaling fiberglass can be very harmful. Many manufacturers like 3M and Shop-Vac warn and prohibit against the use of these filters for face masks.” Another issue with HEPA filters is that they must remain intact in order to filter at max efficiency.

There are many references to large manufacturers of vacuums and air filters. Says Veran, "HEPA filters use hundreds of thousands of fiberglass fibers — incredibly small and sticky for particles that try to pass through them. This tight weave of fibers then captures particles larger than 0.3 microns in size. For a frame of reference, a human hair is anywhere from 50 to 100 microns in diameter, so we’re talking about unbelievably small particles being trapped in the fiberglass fibers."

2. Tissues

Another type of filter to avoid? Tissues, as this is not a very effective option. In general, tissues will make it more difficult to breathe. If you have to remove the mask to breathe more air while being in public, it becomes counterintuitive.

“I do not think tissues offer much filtration efficiency. But if you do go with this, I recommend folding them to increase the protection in filtration,” advises Veran. 

3. Fiberglass

“Fiberglass is the most dangerous object I have heard of,” Veran warns. “Any items that can be easily deteriorated from becoming wet or sprayed with chemicals should be avoided.”

If the material is easily affected by these circumstances, the fibers of the fabric will tear away and can be inhaled if used, or just offer much less efficient filtration.

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What are the best types of filters to use on our face masks?

While HEPA filters, tissues, and fiberglass filters are counterintuitive to keeping ourselves safe, there are a few other materials you can try. Keep in mind that any filter that has been NIOSH approved is much more reliable to use in comparison to buying from an unregistered manufacturer. 

1. Polypropylene

“I would say polypropylene would be the best filter, as it offers more filtration,” suggests Veran. However, the problem with these filters is that they are less common and harder to find.

2. Coffee filters

Interestingly enough, while it's not ideal, coffee filters also aren't the worst option. According to Veran, “Coffee filters are more accessible and slightly better to use because it offers slightly higher filtration.”

3. Anything ending in "95"

P95 and R95 filters have the same filtration efficiency as N95 filters, but they provide additional protection from oil particulates (oil-based solutions that become airborne, like pesticides).

Says Veran, "In regards to the best filters to use, besides polypropylene filters, I would recommend the use of N95 filters and R95 or P95 filters. The Number 95 is in reference to the filter's ability to filter 95 percent of ultra fine particles that pass through it. A N95 filter is the same concept as an N95 respirator, but the respirator is a whole mask while the filter is a small individual piece of its own.

The P95 is semi-resistant to oil while the R95 is strongly resistant. These two respirators are typically more expensive than N95s for the extra protection that they provide. For consumer use and most healthcare settings, both of these respirators are unnecessarily excessive, especially if you are just trying to avoid viral infection but provide the best protection."

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How often should you replace a face mask filter?

“A standard N95 filter, not N95 respirator, can be used for up to 50 breathable hours or approximately 3-4 weeks,” Veran advises. So, if you're using a repurposed filter like coffee or polypropylene, it should be changed every week, depending on how frequently it's used. 

While it may be tempting to reuse a filter after you wash it, this should be avoided. Adds Veran, “Any form of washing a filter will destroy or weaken the fibers, which will render the filter useless and inefficient.” 

Where can you find filters?

In general, you want to make sure you're using filters that have been scientifcally tested and approved for breathing filtration.

“Filters that are NIOSH approved are always the safest bet. I recommend contacting the manufacturer of any filter you use directly to ensure you can receive the genuine filters and proper instruction,” suggests Veran.

Luckily, you can purchase the appropriate filters online. Here are a few suggestions:

1. Polypropylene Fabric Face Mask Filters (10-Pack)

These filters are individually sealed, hand-cut fabric filter inserts for homemade masks that have a pocket.

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(Etsy, $8)

2. PM2.5 5-Layer Filters For Face Masks (3- or 5-Pack)

Stocking up on these filters is a great bargain, since they come in multiples and are very affordable.

(Etsy, $4.50+)

3. MERV 13/PM2.5 2-Layer Filter Inserts

Made of 100 percent high-performance Tribo-Electric synthetic media, which is a special blend of cotton/polymer micro-fibers that gets woven tightly together, these filters create a barrier to prevent particles from getting through.

(Etsy, $1.50+)

4. Ministry of Supply Melt-Blown Polypropylene Filters (10-Pack)

These custom-fit replacement filters have been independently tested by Nelson Labs using an ASTM standard for filtration media to provide higher than 95 percent Bacterial Filtration Efficiency (BFE).

(Ministry of Supply, $20)

Once you find the best filter, there's one piece of advice to keep in mind when sewing it into your face mask: When sewing a mask together, you need to avoid puncturing the filter with the needle since each hole decreases the filtration efficiency."

RELATED: How To Make Your Own DIY Face Mask To Protect Against Coronavirus

Aly Walansky is a NY-based lifestyles writer who focuses on health, wellness, and relationships. Her work appears in dozens of digital and print publications regularly. Visit her on Twitter or email her.