Your Most Pressing Questions About Masks, Answered by CR's Chief Scientist

Do you need a filter? What about a valve? Can you just use a bandanna? Here’s what you really need to know.

people wearing face masks iStock-1227056604

With COVID-19 still spreading in the U.S., masks have become a daily part of American life. In a nationally representative survey CR conducted in July, 85 percent of Americans said they wear a mask in indoor public spaces “always” or “most of the time” (up from 75 percent the previous month). But consumers still have a lot of questions about masks, and it’s not always easy to find evidence-based answers. We asked CR’s chief scientific officer to weigh in.

You can use the links below to jump to a specific question and answer. Do you have a question we haven’t answered? Leave us a comment, or email

James Dickenson


What's the difference between a KN95 mask and an N95 mask? And how are they different from surgical masks?

The first question is fairly straightforward. “KN95” designates the particle filtering standard established by government regulations in China. “N95” designates the particle filtering standard established by the U.S. government in its regulations.

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The “95” in both terms denotes the minimum percentage of particles (95 percent) that are 300 nanometers (nm), or 0.3 micrometers, and larger that the face mask can block. Therefore, N99 masks, another type of mask, block at least 99 percent of particles 300 nm and larger.

A surgical mask is a relatively loose-fitting protective mask, which does not provide assured protection for the wearer from inhaling airborne particles. Essentially, these masks provide protection only from large droplets or sprays of fluids. They can also help protect others if the wearer is contagious.

If you wear a surgical or surgical-style mask, be sure the side with multiple folds on it is facing away from your mouth. The white side of a surgical mask is generally the side that touches your face, while the color (often blue) part faces outward.

At first we heard that masks only protect other people. Now we're hearing that they may actually protect the wearer. Is that true?

A properly fitted mask can provide some added protection over a poorly fitting mask for both the wearer and other people. The primary intent of mask use is to suppress the spread of virus from the wearer to other people. Because COVID-19 can be spread by people who display characteristic symptoms and by those who do not exhibit any symptoms, broad mask use is encouraged to minimize the spread from those who are sick (or potentially sick) to others.

The mask, if worn properly and consistently, also helps protect healthy people from catching the disease when they are in close proximity to people who are sick. It may also provide protection to the wearer from aerosols that persist in poorly ventilated environments, such as an elevator.

Information about how long virus-carrying droplets can persist in the air is being updated regularly. Some research suggests that droplets can remain airborne for multiple hours. So do your part to protect yourself and others by wearing well-fitting, protective masks.

I see people wearing masks that don't cover their nose—is that okay?

The simple answer is NO. Wearing a mask, in part, is meant to protect your respiratory system (your lungs, throat, and sinuses) from direct exposure to airborne droplets and particles that may contain the virus.

To do this, one must protect the primary entry points to your lungs and throat—your nose and mouth. Therefore, leaving your nose exposed will provide an easy pathway for airborne particles to enter your system (by inhaling through your nose) or for droplets to exit your system (by exhaling, sneezing, etc.), potentially endangering those around you.

Should kids wear masks, or do they not need to because they aren't likely to get sick from the virus?

Despite an abundance of misinformation asserting that babies and children are essentially immune to the disease, COVID-19 can and does affect kids, sometimes quite profoundly.

The current thought is that children 2 and older should wear masks when entering public spaces or engaging with people outside their household, much the same guidance that adults receive. The American Academy of Pediatrics has also provided advice on how to get kids to become more comfortable with wearing masks.

What if I don’t have a mask with me? Will a handkerchief or bandanna, or even pulling a T-shirt up over my mouth and nose, offer any protection?

Generally speaking, covering your nose and mouth with a multilayered piece of cloth, such as a bandanna doubled over, will be better than nothing at all. However, one should try to acquire a face covering that will provide sufficient protection.

You should get into the habit of having a mask with you whenever you go out—just like remembering to take your keys, take your mask, too.

What’s the best or safest fabric to use for a mask? Are all masks equally effective?

One of the primary goals of constructing an effective mask is to force the air that you inhale or exhale to travel the longest path through the mask, encountering the most obstacles (or places that will trap airborne droplets, aerosols, and other particles) as possible.

One way to do this is to make masks out of different kinds of high-density, high-thread-count fabric. Crafting a homemade mask with multiple layers of different fabric can provide relatively good filtration and, hence, good protection. You can spot-check your mask by holding it up to a light or a bright window—very little light should pass through.

Keep in mind: The issue is not fundamentally the constituent material from which the fabric is composed. Loosely woven cotton fabric is not recommended; however, densely woven cotton fabric often is recommended as a mask component. In general, fabrics with dense weaves (that is, tightly woven warp and weft threading) and with textured microstructure (cotton and silk come to mind) are particularly helpful when employed in multilayered (3-plus) construction. Single-ply fabrics are to be avoided.

The masks should fit tightly against the bridge of the nose and along one’s face. Masks that have silicone linings along their perimeters tend to provide a seal against one’s skin, providing enhanced protection against air escaping from the edges of the mask.

Should I add a filter to my mask if it has a pocket for one? Are DIY options like coffee filters effective? What about PM 2.5 filters?

In general, adding a filter to your mask would make it more protective, just as a multi-layered homemade mask becomes more protective as you add more layers. The typical pore diameter of coffee filters is 20 micrometers, which is too large to provide meaningful filtration capacity for air filtration.

PM 2.5 filters tend to capture particulate matter that is 2.5 micrometers in diameter, roughly one-tenth the size of that of coffee filters. PM 2.5 filters are more protective in capturing droplets and particulates when worn in conjunction with the types of reusable masks discussed above (ones with filter pockets).

How should I remove and clean a mask? Can I reuse a disposable mask?

Your mask acts as a barrier against infectious particles. That means those particles might end up stuck to the outside of your mask. If you then touch the front of your mask, you could be contaminating your fingers and risk spreading germs. So while you’re wearing a mask, avoid touching its surface. If you need to adjust it, do so using the strings, the elastic, or, at worst, the outermost edges. When you remove your mask, employ those same techniques, and wash your hands immediately afterward.

If you’re using a washable mask, you should clean it at the end of the day rather than wearing it unwashed multiple days in a row. Simply run it through the laundry or wash it by hand by soaking it in a solution of ⅓ cup of bleach in a gallon of room-temperature water and subsequently giving it a vigorous scrub. Be sure to rinse thoroughly and to let it dry completely before you wear it.

Disposable masks shouldn’t be reused. Although shortages of personal protective equipment among healthcare workers have prompted hospitals and clinics to implement strategies for reusing some of these items, these strategies aren’t recommended for consumers.

We have masks with valves in them. Are they okay or better than masks without valves?

These masks might make for easier breathing. But when you wear many types of vented masks or masks with breathing valves, you exhale your germs directly into the air. This defeats the purpose of the mask—to block droplets in your breath from landing on others, and to block others’ exhalations from landing on you. It has led some municipalities, such as San Francisco and Denver (PDF), to clarify that vented masks don’t comply with mask mandates.

Still, for some of these types of masks, the vent or valve also has its own filter, which serves the same function as a plain mask. If you decide to wear a mask with a vent or valve, read the label carefully to make sure it has a filter that will stop droplets from passing through. You can also wear a surgical mask over a valved mask, to cover the vent.

What about face shields? Are they more protective than masks?

Respiratory viruses, including the virus that causes COVID-19, can be transmitted via the eyes, as well as the nose and mouth. So a face shield might provide extra protection against infection. It is not a replacement for a mask but can be worn in addition to one. In one systematic review published earlier this year in the journal The Lancet, researchers found that protecting one’s eyes with either goggles or a face shield could reduce the risk of viral transmission.

Still, the CDC does not recommend that everyone wear face shields every day, as it does with cloth masks. And if you don’t wear a mask under your face shield, small droplets in the air could be carried up under the shield and land on your nose or mouth.

If I’m wearing a mask, do I still need to social distance?

Absolutely. Even with a mask, you should still make every effort to stay at least 6 feet away from people who don’t live with you. Masking is only one layer of protection, and it’s an imperfect one. Social distancing isn’t foolproof, either, but the more layers of protection you can employ, the safer you’ll make yourself and everyone else around you.

Headshot of Chief Science Officer James Dickerson

James Dickerson, PhD

I am a physicist by training and a science communicator by practice. My career's path has taken me from being a high school physics teacher to helping lead a government nanoscience laboratory and now serving as the chief scientific officer for Consumer Reports. On any given Sunday, you can find me watching European football ("soccer," for the uninitiated) or visiting a contemporary art gallery.