What is the best mask?

With the Covid-19 pandemic in full effect, scientists have been working around the clock to find the best ways to stop the spread. One form of protection has jumped to the forefront of the conversation, and that is wearing a mask over the nose and mouth. 

Current research has been showing that Covid-19 is spread by contact with infectious particles from those who are infected. That means fluids, such as saliva or mucus, from an infected person must come into contact with the membranes, such as eyes, nose, or mouth, of an uninfected person for the disease to spread. Since the virus sheds in the upper respiratory tract, any time an infected person breathes, speaks, coughs, or does anything to push air through their mouths, they expel tiny and usually invisible droplets. These droplets can linger in the air for hours and potentially infect someone who breathes in enough of them.

Research on mask materials

There has been some recent research in labs on different materials to make the best homemade mask. This experiment just published in Physics of Fluids simulated real-world conditions with a manikin that coughs out particles and wears masks made of different materials. They measured how far droplets traveled from the manikin’s mouth with no mask, a bandana made of stretchy t-shirt material, a folded handkerchief made of cotton, a commercial “cone-style” mask, and a stitched mask made of quilting cotton.

With no mask, the droplets traveled about 8 feet, farther than currently recommended social distancing guidelines. The bandana slowed particles a little bit, reducing spread down to 3 feet 7 inches. The folded handkerchief managed 1 foot and 3 inches of travel. Droplets exiting the commercial mask went about eight inches and droplets from the stitched mask only went 2 and a half inches.

These researchers concluded that “Loosely folded face masks and bandana-style coverings provide minimal stopping-capability for the smallest aerosolized respiratory droplets. Well-fitted homemade masks with multiple layers of quilting fabric, and off-the-shelf cone style masks, proved to be the most effective in reducing droplet dispersal.”

This other study in ACS Nano looked at many different mask materials on their filtration of tiny particles of salt. The authors wrote that woven 100% cotton worked very well, along with some synthetic woven materials. They also indicated that multiple layers of fabric that do not impede breathability were most effective. This is in alignment with WHO recommendations for healthcare workers.

A wonderful article in NPR also summarizes much of the recent research. They talked to some leading researchers who recommend a cotton mask with a pocket for an insertable filter. Polypropylene is a great material to put in that pocket, since it has static charge that will attract and hold on to particles. Though it will lose its charge after washing, you can rub it to build that charge back up again. Polypropylene is available at Walmart and other stores under the name Oly-fun or spunbound. If you can’t find any, three or more layers of cotton is a good go-to.

Masks are effective

Since it is thought that up to 45% of people infected with Covid-19 are asymptomatic, wearing a mask over the mouth and nose has been recommended for everyone to help slow the current pandemic. Goldman Sachs has estimated that responsible mask use could save 5% of the US economy that will be lost otherwise. States that have widespread mask use have lower rates of infection.

Image source: Science Magazine

Over the past few weeks scientists have been finding practical ways to demonstrate the effectiveness of masks. A study in the New England Journal of Medicine used lasers to illuminate particles exiting the mouth of a speaking person, and found far fewer when the subject was wearing a mask. This video is an excellent demonstration of just how much wearing a mask will reduce the speed of particles exiting your mouth.

Image source: Katie Courley

In a far simpler test, a medical lab technician coughed at a petri dish while wearing a mask and without, as you can see above. While this test shows the presence of bacteria and not viruses, it still gives an idea of the degree a mask can reduce the volume of particles exiting the mouth.

Different categories of masks

There are different masks that solve different problems. Protection from wildfire smoke, for example, requires a different approach than protection from Covid-19. The source of wildfire smoke is from thousands of tons of trees burning, and is composed of tiny particles and gases with a very high concentration in the air so any gaps in a mask could let unhealthy smoke in. Infectious particles of Covid-19, however, are produced exclusively from infected people in tiny amounts compared to wildfire smoke. As a result, just covering the infected person’s mouth is enough to drastically reduce the rate of infection. Putting masks on uninfected people reduces the risk even more.

There are many different categories of protective masks, but here are the basics.

Surgical face masks. These are pieces of disposable fabric held loosely across the nose and mouth. They are not designed to filter large volumes of particles. Rather, they stop droplets of liquid from entering or exiting the mouth and nose. They have been effective for years to help lower the transmission of diseases between healthcare workers and their patients. They are disposable so they can be thrown in a biohazardous waste receptacle after use. Surgical face masks should be reserved for use by healthcare workers.

Respirators. The common N95 mask is considered a respirator, which is any device that forms a seal around your mouth to protect you from particles floating in the air. Most are domes of fibrous fabric held tightly over the mouth and nose. These devices do an excellent job of helping to protect the wearer from most airborne diseases. Like surgical masks, respirators should be reserved for healthcare workers and others who require them for their jobs.
NOTE: Some N95 and other respirators have a small valve in the center. These are designed to protect the wearer from excessive dust in occupational settings for a full eight hour workday. The valve is there to allow moisture to exit and keep the wearer comfortable for the many hours they will need to wear the mask. This valve can also allow infectious particles to exit and should NOT be relied upon to reduce the spread of Covid-19.

Cloth face masks. Cloth face masks have become very popular during the first half of 2020. These serve the same purpose as surgical face masks, but can be washed and used again. They can be stylish and are cheap and easy to make. What makes them effective is intuitive— the better they fit snug against your face and prevent particles from going anywhere other than into the fabric is what makes a good cloth face mask. They do not work as replacements for surgical face masks or respirators.

Gas mask. A gas mask is a type of respirator in that it seals over the mouth and nose. Gas masks also contain filtration media that stop not only particles but also different gases. The user’s own breathing is used to draw air through the filter media. Gas masks usually have filter cartridges that must be changed as they become saturated with toxins.

Power Air Purifying Respirator (PAPR). This is a lot like a gas mask except it has a battery to run a fan that propels the air through the filtration cartridges. If you have a condition that restricts breathing, a PAPR is a safer but more expensive choice than a standard gas mask to prevent undue strain on the lungs.

What is not a mask: Halloween masks, other plastic masks, or ski masks with holes for breathing should not be relied upon. Anything that is very hard to breathe through will expel particles at a high rate of speed, which is not the best mask.

Putting masks to the test

The proper way to test a material’s ability to stop particles like viruses is a fairly complex process best handled by skilled technicians at professional laboratories. But that doesn’t mean we can’t learn a little about how breathable a mask is going to be outside of the lab.

One of our engineers, Machiko Taylor, decided to do a little mask testing herself. She got masks from two different companies, along with a surgical mask and an N95 mask. Then she took out her infrared camera to learn a little more.

Machiko is our Lead Production-Line Operator and Machining Specialist so she knows a lot about how these things work. She used the different temperature of inhaled and exhaled air to get a gauge of how air moves through the masks. “When inhaling, darker spots are where ambient air is sucked into the masks,” she says. The ambient air, which is cooler than the breath, cools off the mask. Therefore on the inhale, dark spots represent areas that are easy to breathe through. 

Exhaling is the opposite because the breath has been warmed by the body. Machiko tells us, “Orange is where the air is coming out from the mask.” However, if we see white areas on the mask during exhale, those are places where air is trapped and warming the fabric of the mask. In an easy-to-breathe mask, it would mix with ambient air and show an orange color. 

So, in summary, a mask that is easy to breathe through will be dark on the inhale, and orange on the exhale.

Mask A
Mask B

Mask A is made of polyester and nonwoven polypropylene, while Mask B is made of rayon, nylon, and spandex. The material in Mask A allows for less restricted air exchange. Less restricted air exchange is not equal to or even correlated with particle filtration so this doesn’t necessarily tell which mask is safer, just which is more breathable. 

However less restricted air exchange means more surface area of the mask is being used. Machiko says allowing the breath to pass through a larger surface area “decreases the overall velocity” of particles exiting the mouth, which means they have “a chance to disperse before getting to other people.” In other words, even if a mask has a high degree of filtration, if there is breath blasting out of the sides at high velocity, the virus spread isn’t minimized.

Here are the masks compared to the surgical mask and N95:

You can see that the surgical mask and N95 are darker on the inhale and more orange on the exhale, which would make sense since both of them were tested in labs to be effective.

When to wear a mask

Unless you are under 2 years of age, are having trouble breathing, are unconscious or otherwise unable to remove your mask if you need, the CDC recommends widespread use to reduce the spread of Covid-19. This is particularly true if you find yourself in the same room as someone from another household.

There are some innate complications to wearing a mask around the clock. People who are hard of hearing or rely on lip movements to communicate may find this particularly challenging. Children or people with disabilities may find it difficult to wear a mask for an extended period of time. Many of us work or spend time outdoors away from other people, where the spread of Covid-19 is minimal. In these or other complex circumstances, the CDC recommends prioritizing wearing a mask when social distancing cannot be maintained.

When you do replace your mask, remember to make sure it is on snugly. If your nostrils are exposed, you are not wearing your mask.

Reusing masks

The easiest masks to reuse are cloth masks, which can be washed. The CDC recommends soaking them in a diluted solution of bleach that can disinfect, so be sure it states so on the packaging. Mix about 1/3rd cup bleach with a gallon of water and soak the mask for five minutes. Then rinse it with cool water and put in the dryer at the highest setting until dry, or alternatively hang it in the sunshine. Never wear a wet mask as they are more difficult to breathe through.

If you work in a healthcare setting, the CDC also has some recommendations for sterilizing N95 respirators and similar masks for reuse. However, unless you have access to the proper facilities, it’s best to keep to cloth masks.

Mask features to consider

If you are buying a mask or making your own homemade mask, there are many different fabrics and features that make wearing them a little easier, more convenient, or fun. We have listed a few below for you to keep in mind.

Fit. This is probably the most important feature of your mask. The better it seals to the sides of your face the less particles will exit at high speed. You can use the nylon material from pantyhose to increase the seal against your face and improve filtration.

Water resistance. Wet masks are hard or impossible to breathe through, so a mask that has an outer layer to protect from rain or other moisture can be useful. Some masks are moisture-wicking, water resistant, or have other ways of staying relatively dry.

Particle filtration. Most people who make masks haven’t gone so far as to send them to a lab to see how well they filter particles, so it can be hard to know what protects best. Experts at Johns Hopkins University recommend a thick and non-stretch fabric, but say that cotton is a good place to start. Anything between your mouth and the world helps—just be sure you can breathe easily and comfortably.

Antimicrobial treatments. Tiny bits of silver or other coatings can slowly kill viruses and other pathogens, so getting a mask that is less likely to be contaminated is always a little better.

Nose clip. This feature is very important for those of us that wear glasses. If there is a poor seal between the mask and the nose, breath can be deflected up behind your glasses and impair vision. A nose clip that fits tight around the bridge of your nose can both stop this nuisance and make your mask better sealed against your face.

Neck loop. When not in use there is a risk of your mask cross-contaminating with any surface you set it down on. Masks with a loop hang around your neck when not in use.

Snugness. It’s important to be sure that your mask does its best to prevent particles from entering or exiting your breathing zone. Any mask should fit snug against the cheeks, under the jaw, against the underside of the chin, and on the bridge of the nose.

Color. Pick a mask that goes well with your skin tone and clothing choices.

Design. Wearing a mask with interesting patterns, messages, or artwork gives you one more place to express yourself.

 

We hope that helps on your quest to find the perfect mask for you. Just like seatbelts and bicycle helmets, they can help to make life a little safer.

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