A Scientist’s Thoughts on DIY Masks

Disclaimer: This post is intended to provide the current (at the time of writing, mid-March 2020) scientific evidence on the novel Coronavirus, paired with thoughts specific to the sewing community. This is not medical advice. If you have doubts on how to behave, whether you should isolate, etc., ask your doctor, not me. In addition, a note to my fellow scientists: this is supposed to help the layperson understand, so pardon my simplifications.


In Summary:

  1. SARS-Cov2 spreads via droplets in cough and sneezes produced by an affected person. If said person wears an appropriate mask, they may prevent others from getting infected.
  2. Given the shortage, disposable surgical masks and respirators should be left to medical personnel and people in need (for example, patients with COVID-19).
  3. Consider making a mask yourself, using tightly woven cotton in multiple layers, and incorporate filtering materials.
  4. Hygiene and avoiding touching your face are much more important and should be the first line of defense. Masks don’t make you immune, so don’t behave as if they do.
  5. Regardless of masks, practice correct social distancing to protect yourself, your family, and your community.
  6. Always defer to information from the health authorities, and make an informed decision that is right for you.

My native Italy is in panic. All nonessential businesses are closed, people are locked in their houses, and even discouraged to go out to grocery shop. City dwellers cannot leave, and rule breakers are facing steep fines and jail time. On the other hand, Japan, where I live now, has had substantially fewer cases, despite a similar demographic makeup and having received a lot of flack as a consequence of the Diamond Princess debacle (hindsight is 20/20). So, what gives? What is happening? What should you do? And, since I know this is what we all want to know, do masks work?

About the virus:

SARS-CoV-2 (this is the name of the virus, and COVID-19 is the name of the syndrome this pathogen induces) is a new type of Coronavirus (no relation to the beer). This kind of viruses has two different hosts before it reaches humans; in this case, the primary host is likely to have been bats, and the second pangolins or ferrets, though it’s likely that different intermediate hosts have been implicated. I’m not going to get into the details of where the spread originated from, as this is still debated (and possibly not the wet market in Wuhan everybody wants to blame). Since the first case, in December 2019, the virus has spread globally, and COVID-19 has been declared a pandemic (meaning that it has spread worldwide). Countries have been way too slow in taking this seriously. Surprisingly, Japan took moderate actions very early, and the exponential increase in cases has been so far averted. Italy, on the other hand, oscillated for days between different approaches, and this delay in the lockdown has most likely caused a dramatic increase in number of cases (for more details on the math, but not in a scary way, look here.) This apparently draconian measure is the only weapon we have to fight the outbreak. Now, data shows that only a minority of cases are lethal, but keep in mind the following.

The virus is spreading very rapidly, not as rapidly as measles (#vaccinate), but current evidence suggests that’s more infectious than the flu. An infected person is most infectious when presenting symptoms. However, asymptomatic (no symptoms ever) and/or presymptomatic (no symptoms yet, but may develop later) people can still spread the disease, although the exact rate of contagion is uncertain. The most sensitive demographics seem to be the elderly and people with pre-existing conditions and the immuno-suppressed. So, you may catch it and have mild symptoms or no symptoms at all, but your grandma may not survive.

What should I do?

I’m not one known for fear mongering or alarmism. Having said that, I find the emergence of a new zoonosis (an animal disease which then infects humans) always very concerning, and the impact on people’s lives, society, and the economy worries me deeply. We have been caught completely unprepared to deal with a pandemic. To make a difference, practice social distancing, wash your hands very frequently (and I mean VERY, possibly every time you touch a surface you don’t know), and avoid touching your face especially eyes, nose, and mouth. If you do need to go to work, especially if by transit, try touching the fewest possible surfaces and wash your hands immediately after reaching your destination. Disinfect your phone thoroughly with Ethanol, at a concentration of at least 70%.

What about masks?

Masks basically don’t do sh*t when it comes to filtering anything except maybe allergens (pollen is about 6 microns, but viruses are generally about 20 nanomers in diameter — much, much, much smaller). Let me explain. Surgical masks, the thin, papery types (actually made of polypropylene), are used in surgery to prevent infecting the patient during the surgery (because, and I know this may sound shocking, surgeons are not sterile, and nor is the operating theater). They don’t protect the wearer, they protect the people around them.

If you are sick:

  1. You should really just stay home, unless you are going to the hospital.
  2. You may slow the spread of whatever is that you are carrying by wearing a mask.

Why is that?

This is because this particular virus can be spread via tiny droplets released when a carrier sneezes or coughs, and these droplets would be at least partly be caught by the mask. Droplets don’t have the ability to stay in the air, and fall to the ground almost immediately. SARS-CoV2 is not particularly good at being airborne, when compared with for example measles, and even the WHO insists that additional evidence is required to confirm if airborne transmission in the form of aerosol (small particles floating around in air) is possible.

Surfaces are also a very common mode of transmission. For example, if an infected person sneezes in their hand, and then presses the elevator button, and then a non-infected person touches the same button and then their face, the virus could be transmitted… hence the stress on hand washing. Because we don’t know how long the virus stays on surfaces outside a carrier (minutes? hours? days?) it’s best to use precaution. One paper suggests highest survival of this pathogen on plastic and steel, where the virus was still detected after 72 hours. (Keep in mind this is data from 1 study only, and in controlled laboratory conditions, and these findings are therefore to be taken critically).

For the sake of argument, let’s pretend for a second that aerosol transmission was the predominant route in this case. If you want to protect yourself from the airborne component, then you would want to get a respirator (I’m doing a reductio ad absurdum here, please don’t go and get a respirator), and not a surgical mask with zero filtration power. In addition to that, any mask, not just respirators, needs to fit properly, with no leakage, to be effective.

I honestly don’t think there is enough risk at the moment to justify the general public using masks, let alone respirators, so please, PLEASE leave them to the medical personnel and to people who actually need them. In particular, think of the doctors and nurses in your hospitals: they are exposed day in and day out to the pathogen, and have started to get sick, and even die. Surgical masks should be changed frequently, and are useless when wet. Even in Italy, a country that has one of the best healthcare systems in the world, there is a shortage of all single use medical protection equipment, not to mention of ICU beds. Italian doctors have reported that the Europe-wide shortage of single use protective equipment has caused a spike of medical professionals hospitalized (you can listen to the first hand testimony from an Italian physician on the NYT The Daily podcast). You don’t want that in your own back yard, do you?

If, despite having no symptoms, you still want a mask, make one, don’t buy one. There are a couple of patterns easily available:

  • This one from Freesewing.org, which is generated based on head circumference measurements you enter. (I like this one a lot and have made it for allergy prevention.)
  • This one shared by our friend Katie, who is also a physician.
  • Here is a video showing a no-sew method for making a mask. It’s in Japanese, but the video is clear even if you don’t speak the language.

Note: some classic studies suggest non-woven fabric is marginally better at filtering air, but this was tested on with bacteria, which are an order of magnitude larger than viruses. Two or more layers of tightly woven fabrics, especially when a material with filtering capabilities is placed in the middle (vacuum cleaner bags do come to mind) are going to give you a similar level of protection to the disposable surgical masks. It is CRUCIAL that you change the mask every time you touch it and especially if you remove it (to blow your nose or to eat), and you disinfect them. Remember that every time you touch your mask, even just to readjust it, you are contaminating it. If you are sick, this mask should definitely be treated as biohazard. When you remove the mask to wash it, wash your hands afterwards.

At home, you can use a domestic pressure cooker to disinfect your masks or just steam over boiling water for 20 minutes. Boiling also works, but it may damage elastic and the non-woven fabric sandwiched in the middle. Using tied ribbons instead of elastic would serve you well if you’re planning to boil the masks.

(By the way, if you are interested in the lowdown on hand sanitizers — which DIY versions are good, which bad — look no further than this video from a fellow scientist.)

Social distance is more important than masks:

Heavy-handed measures of community containment, like in Hubei, and social distancing do work with a disease which is transmitted between subjects in close contact such as this. This is not a matter of opinion but a scientific fact.

Please remember that wearing a mask should really not be a first line of defense. Don’t relax your social distancing, and by all means DO NOT think that since you masked yourself you can engage in at-risk activities in the middle of an epidemic.

Why flattening the curve is important. Source here.

The problem is that COVID-19 is spreading rapidly, more than the seasonal flu. Unlike the flu, we don’t have any immunity against it, and no vaccine (it is, after all, a novel Coronavirus). This means that if we let it roam free there will be an exponential increase in cases, too much for the health services to handle, and a consequent increase in deaths.

This brings us once again to what YOU can do. It’s very simple, besides washing your hands etc., etc.: just.stay.home.if.you.can. Social distancing is the only, and I repeat, the only way we can fight the spread of the disease. Let me repeat once more: if you wear a mask and then don’t wash your hands or even worse go on hugging people, go to the movies, say “I’m wearing a mask but I still want to live my life normally”, you are contributing to the spread of the disease. You may not care for yourself, but you should. Not being in at risk category doesn’t mean you can’t get it, or pass it to someone who is. And even if you don’t think this is a big deal, that the majority of cases are mild to asymptomatic, then think that if we don’t flatten the curve, expand the time constant, health services will collapse, and medical professionals will have to make the choice of whom to save.

Some parts of the world are asking for home sewists to make fabric masks for hospitals and front line workers. This is a time to stick with local information: find out if homemade masks are required in your area, and make sure you sew something that meets their requirements. This is our time to shine — and also, wash your hands, you filthy animals!

Additional references:


Emilia enjoys black outfits, word puns, and transforming her apartment into a greenhouse. When she is not sewing, she is a researcher in the field of Neuroscience. You can find her on IG @emilia_to_nuno and on her blog.


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