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Buying guide for Best filter inserts for masks

A cloth face mask is economical because it’s washable and available in just about any pattern you can think of. It’s a great option for anyone venturing into public spaces in times of uncertainty, but with just two layers of cloth, its effectiveness is limited, and virus particles can still pass through. A filter insert improves the effectiveness of cloth masks tremendously.

When slipped into the pocket between the first and second layer of a cloth face mask, the right filter insert can improve the filtration of particles by as much as 35%. At this point, hundreds of manufacturers are bringing filter inserts to market, and from the outside, most look exactly alike. A few considerations can help you determine which insert offers the best filtration of airborne particles.

The face mask market is on track to pass $7 billion this year — a $5 billion leap — and filter insert sales are trending steeply upward, too.

Key considerations


Do you primarily use cloth masks that have a pocket for a filter insert? These filters are designed especially for this type of mask and don’t work well with other types.

For instance, stapling a flat filter insert into a KN95 mask or medical mask is redundant, clumsy, and won’t improve the efficacy of these types of masks. Using the filter insert alone is also not recommended. These are designed to work in concert with a cloth face mask.


Keep in mind that no material — or number of layers — will protect you 100% from a virus. Choose a combination of materials and layers that permit good airflow so that you breathe comfortably, follow additional social distancing guidelines for public spaces, and you will drastically reduce the chance of contracting or spreading a virus.

Did You Know?
Polypropylene is the main material in N95 masks, but it can be found in some filter inserts for cloth masks.


At first glance, all filter inserts look exactly alike: white or light-colored, rectangular, and flat. Consider the following features when choosing a filter insert.


The Centers for Disease Control (CDC) recommends that filters have multiple layers of cloth or paper to effectively trap airborne particles. Filter inserts have three to five layers of material, with the roughest (or fuzziest) layer in the center. The center layer is often activated carbon, an inexpensive but effective material that traps particles.

And each layer needs to be a different type. Choose a filter insert with combinations that include a smooth outer layer on both sides (which is easier to slide into the mask pocket), and a rough or felted inner layer, which does a better job of trapping tiny particles.


Filter inserts can be made of several different types of material. If there’s a common quality among these filters, it is this: fuzziness. Smooth material doesn’t do as good a job of trapping particles and water droplets as rough or fuzzy material.

Polypropylene: The CDC recommends a polypropylene layer of material. Polypropylene fabric can hold an electrostatic charge (think static electricity), and that static helps trap droplets, both when breathing out or breathing in.

Activated carbon: Similarly, activated carbon filters trap many types of airborne particles, including dust, mold, and smoke. Used alone, they will not trap viruses, but they are effective as part of a layering system.

HEPA: A high-efficiency particulate air (HEPA) filtration layer is another consideration. These can filter out up to 99% of particulates, but air doesn’t pass through them as easily as it does carbon filters. If you’re looking for this type of filter insert, make sure that the label states that it is HEPA, certified by the Institute of Environmental Sciences and Technology (IEST), and not “HEPA-type” or “HEPA-like” which may not be as effective.

PM rating

Particulate matter (PM) is a term used for the mixture of solid particles and water droplets in the air we breathe. These particles are various sizes: some you can see, like smoke or heavy dust, and others you can’t see, like molds or super-fine particulates. The EPA has two different ratings for particulate matter that can be inhaled:

  • PM10: Particles that measure 10 microns or smaller
  • PM2.5: Particles that measure 2.5 microns or smaller

Virus particles are almost universally smaller than 2.5 microns, so a filter insert with a PM2.5 rating is ideal for effectively blocking them.


The filter insert should fit the contours of your cloth face mask. Too big and the filter will fold and crinkle inside the mask pocket. Too small and particles will escape around the edges of the filter and through the cloth layer.

Filter inserts are available in sizes that roughly match commercially available small and large cloth face masks. Custom-cut inserts for specialty masks, such as cycling masks, are available and designed to conform to the interior of these types of masks.


Ease of use: Anyone who has struggled to slip a layer of felt into the pocket of a cloth face mask knows the frustration of trying to insert, straighten out, and later remove that additional filter. Look for filter inserts with an outer layer that isn’t too fuzzy, so that the layer doesn’t attach itself to the inside material of the cloth mask.

Frequency: Some filter inserts are advertised as usable for up to three days. This is helpful in situations where you may not be able to change out a cloth mask as often as you’d like. But cloth masks ideally should be replaced with a clean mask each day, and filter inserts need to be removed before the masks can be washed. It’s safe to say that you will need to change the filter insert every day.

That creates another important consideration: how many inserts you should get at once.  Getting just ten inserts is fine when you’re trying to find the right size for your cloth mask. Once you’ve settled on a size and style, save time and money by choosing a 30- to 100-day supply.

Filter inserts with multiple layers should be firmly sealed around the edges so that the layers don’t separate.



Cloth face mask: ililly Black Face Mask
This washable cotton face mask features a side-entry pocket that a filter insert can be easily slipped into and out of. It’s contoured nicely to the face and has an adjustable nose wire to prevent slipping. Adjustable ear loops keep the mask snug on the face.

Did You Know?
Air flows less freely through HEPA filter inserts. They’re great for filtering allergens, but they might be uncomfortable to wear when exercising.

Filter insert prices

Filter inserts for cloth masks are sold in multipacks, with the price per mask dropping as the quantity increases.

Inexpensive: In general, a 10-pack of filters that claim a PM2.5 rating costs as little as $3 to $5, but most are one size fits all.

Mid-range: For about twice as much, or $6 to $12, you can choose from small or large filter sizes. Custom insert replacements for cycling masks can be found in this price range, too.

Expensive: For those who want to stock up with packs of 50 to 100 filter inserts, expect to pay $13 to $26.


  • Wash your hands before inserting a new filter into a cloth face mask.
  • Remove and discard the filter insert at the end of the day. Wash the cloth mask.
  • Choose the right size. A cloth face mask must cover your nose, mouth, and chin, so a filter insert must be large enough to fit most of the face mask’s area.
  • Avoid touching your face mask while wearing it. Don’t shift the mask around on your face.
  • Choose a filter insert with a PM2.5 rating. It’s designed to filter particles smaller than 2.5 microns. This type of filter is effective for about 12 hours of wear before it needs to be replaced — about two to three days of average mask use.
Use a cloth mask that fits your face comfortably and snugly, and purchase filter inserts that correspond to the size of the mask. You’re much better protected when the filter and mask are both the right size.


Q. I find it much easier to put in a smaller filter insert and center it on the mask. Is this okay?

A. If the filter insert is too small, air particles will be drawn in or pushed out around the edges of the insert, reducing the mask’s overall effectiveness. Use the appropriately sized insert. You might find it easier to get the insert into a side-loading pocket by reaching two fingers and your thumb through the opposite side of the mask and gently tugging the insert into the pocket and into place. For a top-loading pocket, try gripping the filter insert from the outside of the fabric and tugging it into place.

Q. If a filter insert doesn’t guarantee 100% protection against virus particles, why should I bother using it?

A. Using a two-layer cloth mask alone, with no additional filtering, may protect users from 70% to 90% of virus particles, according to a recent study published in Risk Analysis. Adding a five-layer, PM2.5-rated filter insert can instantly increase that protection to between 95% and 99%. A mask isn’t perfect protection, but with a filter insert it’s highly effective at protecting you and others from virus transmission.

Q. Can I wash a cloth face mask that still has a filter insert in it?

A. I’ll be the first to raise my hand and admit that I’ve accidentally done this. Washing a face mask with the insert still in place probably won’t hurt the mask, but the filter insert will no longer be effective. Remove the insert and rewash the mask. Install a new filter insert.

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