The Science and Tech of Face Masks
By: Thomas Smith
Tags: Covid 19, Explainer, Face Mask, N95, Science

The Science and Tech of Face Masks

I put my money (and my body) on the line to teach you everything about COVID-19 masks

Images courtesy the author

When the CDC starts publishing sewing tutorials, you know things have gotten weird. As COVID-19 has spread worldwide, though, that’s the strange new world we’re living in.

When the COVID-19 crisis first began, the Centers for Disease Control in the the United States, and the World Health Organization internationally, came down strongly against healthy citizens wearing face masks. In some ways, that made sense at the time. Most masks don’t protect the wearer from infection, and there’s a risk that they’ll provide a false sense of security.

Just as seatbelts and airbags make people drive faster, wearing a face cover can convince people that they’re fully protected from the coronavirus, prompting them to go out more, touch their face, and skip steps that really do protect them, like the simple step of washing their hands. Initially, there was also the concern that people would buy up medical grade masks, taking these out of the hands of the front-line medical professionals who actually need them.

As the coronavirus crisis wears on and social distancing measures continue to intensify, the CDC has made a dramatic about-face. Acknowledging that masks protect others from you, even if they don’t protect you from others carrying the virus, the CDC now recommends that Americans wear a face covering any time they go outside. Several jurisdictions — including Los Angeles — have quickly enshrined this advice in enforceable laws and ordinances.

Like so many things with COVID-19, we could likely have learned this lesson much earlier if we just looked a bit beyond our borders. Asian countries have made masks a cornerstone of their coronavirus response from day one. And in places like Japan, it’s customary to wear face masks throughout the cold and flu season even in normal times, as a social gesture if not a medical one.

In any event, with the CDC’s dramatic reversal, Americans are suddenly getting a crash course in face coverings. Minutiae like the difference between cloth masks and medical grade masks are now acceptable quarantine-unit dinner conversation. Extremely technical terms like “N95” are suddenly common knowledge — and fodder for political squabbling.

The American’s credit, our civic organizations and individuals have mobilized around masks in a way that’s likely possible nowhere else. Church groups and the like are sewing cloth masks en-mass, and mask drives have resulted in donations of medical grade masks — often sourced from shuttered businesses or peoples’ garages — to hospitals across the country.

How do face masks work, anyway? How are they made? What are the different kinds, and how do they differ? How can you make your own? All of these questions are suddenly on millions of peoples’ minds. So I decided to dive in and help you answer them.

Doing so required wiring money to China, spraying myself in the face with a former chemical warfare agent, and relearning some middle school Home Economics skills I thought I’d never need to revisit. Let’s dive in together and take a look at masks in all their various forms.

Let’s begin with first principles. There are essentially three broad categories of masks available today: respirator masks, medical grade surgical masks, and cloth masks.

Respirator masks are the hardest to come by, and the most politically fraught. These are the fabled N95s that you hear mentioned ad nauseum on the news, and that authorities are encouraging citizens and companies to donate — forcibly or otherwise — to front-line first responders.

Why are these masks so important? Unlike all the other options on the market, they provide the wearer with a measurable level of actual protection against the COVID-19 coronavirus, and other airborne pathogens. The N95 designation means that the masks block 95% of particles under .3 microns in size. That includes many of the droplets that carry viruses and bacteria, including, many scientists believe, Covid-19. So if you’re wearing an N95 mask, you’re actually protected against the virus, even if it’s floating in the air all around you.

N95 masks are believed to protect the wearer from the virus

The catch is that for N95 masks to work, they have to fit properly. The masks’ ability to block particles is worthless if there’s a big gap around your nose (or your beard), and air is flowing through it. In a medical setting, front-line workers are routinely fit-tested, to ensure that their N95 and other respirator masks are actually providing protection.

The process for a fit test is relatively straightforward. You have a provider put on their mask, and adjust it properly to fit their face. You then place them in an environment with detectable particles of around .3 microns. If they can detect the particles, then they’ve failed the test. If they can’t detect them, then the mask is a proper fit, and passes.

I wanted to see how this fit test process works firsthand. I have an N95 mask which was purchased before the crisis, and which I’ve already worn, making it ineligible for donation. So to see how it fits me, I went in search of the materials necessary to perform a fit test.

Most of the time, these tests are performed using pleasant particles. A doctor or nurse puts on their mask, and steps into an environment filled with either a pleasant smelling chemical, or a fine mist of an artificial sweetener, like saccharin. If they can smell the chemical or taste the sweet saccharin, they’ve failed the test.

All the materials required to perform this version of a fit test were sold out. So I resorted to the only option still available: stannic chloride. Stannic chloride is a chemical compound originally used as a chemical warfare agent. Even at low (non dangerous) concentrations, it causes immediate (but harmless, if used properly) irritation to the nose and throat, causing coughing and discomfort in users.

It’s often used for fit tests where there’s a concern that a user might fake their results — for example, when they want to get through the fit test as quickly as possible and return to work. It’s easy enough to step into a chamber filled with saccharin wearing an improper mask and say “Nope, I don’t taste anything!”. It’s harder to get blasted in the face with stannic chloride and avoid uncontrollable coughing.

Technically the chemical is usually used for fit tests on N100 or P100 masks, which block even more particles than the N95 ones. But I figured that with stannic chloride, I should at least see a noticeable different in irritation if I wore an N95 mask or left it off, as it should still block a significant amount of the chemical if I was wearing it properly.

And that’s how I found myself stepping onto my driveway and using a little turkey-baster apparatus to spray myself in the face with a former chemical warfare agent (please, don’t try this at home).

The fit test protocol for stannic chloride says that to begin, “the test subject shall be allowed to smell a weak concentration of the irritant smoke before the respirator is donned to become familiar with its irritating properties.”

Aspirator for a stannic chloride fit test.

So I wafted a bit of the smoke out of a tube until it hung in the air, closed my eyes, and stepped through it while inhaling deeply, like an old-school department store shopper trying out a new perfume.

I expected an acrid smell. But my experience of inhaling the smoke was less a smell, and more a sensation: the instant, burning need to cough.

It wasn’t like someone blowing cigarette smoke in your face, where you’re hacking away for minutes. Rather, it immediately induced that feeling that you might get if you’re sitting in a quiet lecture hall, a theater, or another place where coughing would annoy those around you, and you find yourself needing to cough repeatedly anyway. “Irritating” is actually an excellent adjective to describe the overall experience.

I then donned my N95 mask, again following the recommendations from the fit test protocol, and puffed out a bit more smoke. This time, when I walked through it and inhaled, I felt nothing — no need to cough, no irritation, almost no effects at all.

I could smell the vapor a bit now (likely because my mask was N95 and not N100), and it had a pungent, gunpowder-like sulfurous smell. But the irritation was totally absent. Emboldened, I tried blasting my mask several times with the smoke. Still, I felt nothing.

The results were striking. I had assumed that as a layperson, I was probably wearing my mask incorrectly, and some amount of air (and potentially virus-laden particles) were leaking through. But my fit test showed that actually, the mask was surprisingly effective, even with my limited knowledge of how to use it properly. It gave me a new faith in the mask’s ability to protect me from whatever was out there floating around in the environment — whether that’s irritant smoke or the virus-filled remnants of some infected person’s sneeze.

That protection is why N95 masks have become the gold standard during the age of coronavirus. By actively blocking the particles which carry the virus, they provide the kind of protection that front-line healthcare workers need when treating infected patients. It’s also why they’re in such short supply.

Before the crisis, healthcare workers would discard N95 masks like candy. Between each visit with each patient, they would don an N95, and then throw it away after leaving the patient’s room. Even in a construction or other non-medical setting, the recommendation was to wear N95 masks for at most 8 hours at a time.

Now, the recommendations have changed dramatically. Front-line healthcare workers are wearing the same N95 mask for up to 30 days. The FDA has rapidly cleared technologies for sterilizing the masks, making them truly reusable. Absent high-tech solution, some healthcare workers have taken to dousing their masks in alcohol or boiling them to sterilize them and allow them to be used for days or weeks at a time.

Interestingly, N95 masks with a valve (which makes it easier to breath while wearing them) are actually banned in several jurisdictions’ mask orders. This is because the valve allows air that the wearer breaths out to pass unimpeded through the mask. Since the air is not filtered by the mask, N95 masks with valves provide no protection to others around you. If you still want to wear an N95 mask with a valve, go right ahead — just put some kind of cloth covering (on which more below) over the valve to protect others around you in addition to protecting yourself.

While N95s are the gold standard, there’s another option that’s proven nearly as good against other respiratory viruses: the medical-grade surgical mask. These are the little blue or yellow face shields you see doctors wearing in medical dramas, or may have put on yourself if you’ve ever visited a hospital during flu season. Surgical masks don’t create an airtight seal over the user’s mouth and nose like N95 masks do, so initially they were assumed to be much less effective in protecting against the coronavirus.

Recent studies have contradicted that assumption, though. Covid-19 is thought to spread mostly through droplets in the air, which are coughed or sneezed out by a sick patient. Surgical masks provide a barrier against these relatively large droplets, even if they don’t have a perfect seal. They also have the added bonus of preventing users from touching their faces, something that humans do an alarming amount.

As the crisis has unfolded, surgical masks are now considered nearly as good as N95 masks for medical workers. N95s are reserved for procedures where there’s likely to be a lot of coughing or sneezing (like intubating a patient), but otherwise healthcare workers are turning to the more basic surgical mask.

At first, I assumed surgical masks were made from a simple piece of fabric. It turns out they’re actually much more complex, and harder to manufacture. Medical-grade surgical masks have three layers, or plys. The outer layer is usually a waterproof synthetic fabric. It’s there to protect against watery sneezes and coughs, and to trap the big particles on which bacteria and viruses often travel. It also protects against splashes of blood or other bodily fluids during procedures.

A medical-grade surgical mask.

The middle layer of the mask is generally a filter, which traps bacteria and viruses down to 1 micron in size. It’s not as good as the .3 microns that N95 masks are rated for, but it’s still a lot more protection than a cloth mask (on which more below).

The final layer is generally another filter, and is designed to absorb the vapor from the wearer’s own breath, since the masks are generally right against the mouth and nose. Making a medical-grade mask is a challenging task. It requires special equipment, with extruded plastic sprayed through nozzles to create the tiny, sub-micro-size fibers that block particles but still allow air to flow through.

Many surgical masks are made in China. When the country was dealing with its own disease outbreak, most mask protection stayed internal. As China tamped down the virus internally, though, production started to open up — and so did exports to hard hit areas like Europe and the United States.

For previous projects, my company has worked with several manufacturers in China. They’ve helped us make things like product labels, a custom pet product, and thousands of specialized plastic bags. As China flattened its own Covid-19 curve, I started receiving messages from our Chinese suppliers offering a new product: surgical masks. Recognizing an opportunity, the country has pivoted hundreds of factories towards making masks, and is now churning them out at a (claimed) rate of 110 million per day.

At first, I was skeptical about the masks on offer. But as I started to read about healthcare workers in Seattle and New York using garbage bags and bandannas as PPE, I realized that our connections in China could serve an important purpose in the Covid-19 fight. And so I found myself taking on the unexpected role of procuring hundreds of masks from China.

Even in normal times, doing business in China (at least at our small scale) is a fascinating mix of old-school hands-on service and very streamlined tech. We originally found our Chinese suppliers through the ubiquitous marketplace Alibaba. We then developed relationships over time, conducted through email, with both sides likely making liberal use of Google Translate.

Most of our purchases from Chinese factories — masks included — have started with us receiving an email (often out of the blue) from a supplier offering a new product. These generally list a Minimum Order Quantity, a description of the product, and some staged photos of the product in use. In normal times, this might be some new kind of bag or label.

In the age of coronaviruses, these emails feature smiling models wearing face masks, and details about 3-ply construction and factories’ manufacturing capabilities. Many factories go so far as to create an invoice with your company name and details inserted, before even discussing a purchase with you.

What follows is a certain amount of very cordial and responsive email haggling — generally not around the price, but around breaks for quantities, shipping speed, and the like.

I’ve found Chinese factories to be remarkably responsive. I can send an email in the middle of the night on Chinese time, and get a response within hours. The factories often seem to be embedded without local networks, too, which allows them to source products from peers. I could likely ask any supplier for some random product (say, car tires), and within a few hours they’d have a quote and invoice ready for me.

At some point in the process, the transaction moves to a leap of faith — wiring hundreds of dollars to people you’ve never met, in a place you couldn’t locate on a map, and hoping they follow through on their end of the bargain. I say “wiring”, but really no one uses wire transfers — most payments are made either through Alipay or Paypal, to a email address provided by the factory. The total cost includes the product, shipping, payment feeds, and adjustments for any duties the factory must pay.

It sounds crazy to take this leap of faith, especially with bigger orders. But I’ve placed dozens of these orders over the years, and I’ve never had an issue with a factory failing to fulfill an order. If anything, most factories move faster then advertised — the old business adage to underpromise and overdeliver seems alive and well in China.

In this case, I worked with a supplier we’ve used for custom packaging and bags in the past. We agreed to purchase their MOQ of 800 surgical masks, for $310, including door to door air shipping. I sent the money via Paypal, with a promised delivery time of 12–15 days. In less than 7, a case of masks arrived at my door. The company even provided certificates from an independent quality assurance company, as well as an FDA certification, which made me more confident in the masks’ quality.

Even so — and recognizing that I had no idea what I was doing from a medical perspective — I decided to check them out for myself. There are several guides online for testing the quality of surgical masks. One test involves filled the front of the mask with water — if they’re real, the outer layer should be waterproof. My masks passed the test. Another obvious step it to cut the mask in half and ensure that it has three layers — mine did.

I stopped short of conducting a “fire test”, which involves pulling out the inner layer of the mask and trying to light it with a match. I don’t want to add “third degree burns” to the list of ailments my local medical system needs to treat. And besides, these masks weren’t meant for me — we purchased them to donate to the University of California San Francisco.

Months ago, donations of life-saving medical supplies from the general public would have been unthinkable. But as Covid-19 has strained supplies and front-line workers have taken drastic measures, many hospital systems are accepting (or actively soliciting) public donations of PPE, masks included. We donated our masks (minus the ones I removed for testing) to UCSF, where they were accepted by the nurses of the Benioff Children’s Hospital’s Intensive Care Nursery.

ICN nurses at UCSF accept our donation of 700+ surgical masks

UCSF will likely perform their own inspections of the masks (unlike me, they’re qualified to do this), and perhaps perform their own sterilization process. The masks will then likely be deployed in the fight against Covid-19, either to protect patients or visitors to the hospital, or if things get really desperate, to protect front-line workers themselves.

If you have surgical masks — even just a few — you should donate them too. Often the best place to start is with you local hospital — many have donation programs in place. You can also contact your town authorities — my town of San Ramon, California accepts donations in the City Hall parking lot at least once per week. Or you can reach out to a national organization like Operation Masks, which matches people who have PPE with healthcare organizations in need.

Don’t have medical-grade masks to donate (or obscure connections in China)? Or looking for an option to protect yourself, the average citizen? Your best bet is likely to turn to the final type of mask: a cloth face mask.

These masks are increasingly becoming mandatory in cities and states around the country. New York City is adopting mandatory mask laws this week, and many counties in the Bay Area have already made the move. As the world moves to reopen, it’s likely that face masks will be mandatory equipment for more people, more of the time. And for most people, it’s likely that their mask will be a homemade cloth one, not a medical-grade mask like my N95 or surgical masks.

How do homemade cloth masks work? Again, as with surgical masks, the main goal is protect others from the wearer. Cloth masks block your potentially infectious sneezes and coughs, keeping others around you a bit safer — especially in situations like walking through a grocery store or working in an office, where social distancing is often impossible. In some really desperate situations, cloth masks can even be used in a medical setting to protect patients, and the CDC formally authorized the uses at the beginning of the Covid-19 crisis.

So how do you actually get a cloth mask? There are numerous options online, and some high-fashion brands have turned to producing their own. But the simplest solution — and often the fastest — is to make one yourself. That brings us back to the CDC’s pivot towards domesticity, and its templates for sewing your own cloth mask at home.

I went to a very progressive public middle school in a suburb of Philadelphia, which was suspicious of gender norms way before “woke” became a household word. My school required all the female to take shop, and all the males to take Home Economics. So I received several semesters of formal education in sewing, cooking, and other basic household skills. When I saw the CDC’s mask tutorial, I felt fairly confident I could follow it.

Armed with a $9 sewing kit from Amazon and an old cloth dinner napkin, I got to work creating my own Covid-stopping PPE. The CDC’s mask pattern is very easy to follow. You essentially create two big rectangles of fabric, sew them together, and then create little pockets on each side for ear loops.

The CDC doesn’t directly suggest this, but many people choose to insert something between their fabric pieces to add a third layer of protection, much like a real surgical mask. Choices range from coffee filters to Swiffer cloths. Vacuum cleaner bags, it turns out, are the best option for improvised filters. The most important thing is to choose a material which can be easily laundered, or to construct your mask in a way that you can swap out the filter routinely.

For my own mask, I cut out my two pieces of fabric, transforming my fancy Pottery Barn dinner napkin into ugly rectangles with alarming, jagged edges. I then got out my needle and thread, and started sewing them together. Quickly, I realized that my sewing skills have atrophied — a lot.

My stitching work was less Martha Stewart, and more Frankenstein’s monster. Still I managed to hem the fabric and attached it at the top. Then, recognizing my own limitations, I finished the rest of the mask with tape (gaffer’s tape is a good choice), and inserted kitchen twine as my ear loops.

My CDC pattern cloth face mask under construction.

The end result was ugly as sin, and made me look like some kind of a poorly thought-out, off-canon Star Wars character from a forgotten desert planet. But it stayed on my face and covered my nose and mouth — the basic requirements for a cloth mask in the age of Covid. If you have your own sewing machine or even a tiny modicum of hand sewing skill — which I clearly lack — you can probably create something much better and more durable.

And if you can’t, there are likely plenty of people in your neighborhood who can. Through the same motivation that has led to an explosion of quarantine cooking, many people are turning to domestic pursuits to pass the time. Check out the Nextdoor feed for your area, and it’s a good bet that some local good Samaritan will make you a really nice cloth mask for the cost of materials, or even for free.

As with all things Covid, masks are likely here to stay, at least for quite some time. If you have N95 masks available, they’re the gold standard of protection. Unless you’re an essential worker yourself, you’ve worn your mask already, or you’re in a very high risk group, you should donate these masks to those who genuinely are on the front lines.

If you have surgical masks — or have a supplier who can produce them — leverage that. The world will need many millions of these masks to make it through the pandemic, and your local hospital and first responders are likely to embrace a donation of surgical masks with open arms.

You can also consider donating money to a charity or organization with the supplier connections to buy more of these masks — imported or otherwise — for local or national donation.

And for you own protection — or just to have a project — consider creating a cloth mask of your own. You can experiment with different filters and materials. You can even use the mask as a unique expression of your own style — from the high end and posh to the ironic. For some, masks are even a way to wear a big middle finger to Covid on their face whenever they’re out in the world, showing their own breed of solidarity and perseverance through the crisis.

A few months ago, the idea that millions of people who become intimately familiar with a product as obscure as face masks would have seemed bizarre. But the world we’re living in now is bizarre in so many more serious, alarming ways. Masks are one bright area, where we can each take a simple action that directly affects the common good — especially with cloth masks than anyone can make at home.

So get out your needle and thread, consult either your grandma or the CDC (never a line I thought I’d get to use), and start sewing!