Fabric Considerations for DYI COVID-19 Masks


How to make your household fabrics work effectively in your reusable #DIYMask & how to clean them so they are safe to use

An interview with Matteo Borri

By Lisa Rein

April 23, 2020 (will be updated as needed)

New just added April 23: water does need to be almost at boiling to properly sterilize – here’s the paper. We were already telling you this :) See our section on cleaning here.

(Attention New York City residents: You may not have to make your own mask, as you can likely get a free mask from Masks for the Masses.)

TLDR Summary of this article (with links to details):

  • Wear a mask or some kind of covering over your face when you are in public spaces: to protect each other from our germs.
  • Even without any symptoms, we could all be asymptomatic carriers, and need to protect each other.
  • If everyone wears a mask, we actually can all protect each other.
  • Here are some patterns for making your own mask to use with the information in this article.
  • Do these tests to see if the fabric you are considering for your mask will work ok.
  • Clean your mask after every time you use it.
  • Leave your shoes at the door of your home, as infected particles can live on the bottom of your shoes for several days.
  • Write aaronswartzday@protonmail.com with any questions, and we will check with Matteo and the other experts we have access to, and write you back with answers.

Follow these simple steps – to protect yourself and others:

  • check that you can breathe easily through the fabric you are considering (and make sure you can still breathe through it when it is doubled or quadrupled in thickness.
  • double the fabric at minimum and quadruple it (or more) if possible.
  • even with your mask on, remember to still stay 6 feet away from others, when possible.
  • wash your mask every time you come home.
  • try to have two masks, so you will always have a clean one handy.


The CDC has finally confirmed what many people have been saying for months now: everyone should be covering their face with at least some kind of cloth or DIY mask, while out in public, to protect each other from COVID-19.

Since official N95 masks are in such short supply – as even medical professionals are having a hard time getting them – if you don’t already have an N95 mask, it is unlikely you will be able to obtain one anytime soon.

For many folks, that means they’ll have to use a DIY mask or nothing. There are many patterns available, but what are the most important factors to take into consideration when choosing fabric for making your DIY mask?

To help understand what we all need to know, I interviewed our own Matteo Borri, an inventor and engineer who built a laser-powered chlorophyll detector that will be included next Mars Rover.

There are only a few important things to consider when choosing your fabric.  We explain them below, along with some simple instructions for how to test fabrics – and – very importantlyhow to keep your reusable masks clean, once you make them. (As it is not safe to use reusable masks unless you can clean them regularly.)

We are trying to keep this super simple on this page, but for some people it will still be too long, so we have a TLDR version above. and here are the authoritative References we cite, so you can drill down in as much detail as you wish – and rigorously double check that what we are saying here checks out.

If you find anything that should be changed or have suggestions at what could be better explained, please don’t hesitate to write us at aaronswartzday@protonmail.com

Why Wearing A Mask Matters So Much

Upon our learning recently that DIY (do it yourself) masks only work best  when everybody is wearing some kind of mask (because doing so generally will keep people’s spittle & germs from getting into the air and infecting others), we felt like it was important to pass this information – and some other details – on to you as soon as possible.

Although only N95 rated masks can truly protect you from exposure to small airborne droplets that contain the virus , it turns out that if everyone were wearing even makeshift masks, there would be significantly less airborne particles in public spaces. 

In light of all of the information that we were able to gather, it would appear that not wearing a mask is just plain irresponsible at this point.

Whatever your situation is – you need to, at the very least, wear a bandana or a scarf around your nose and mouth to protect others, in case you could be an asymptomatic carrier.

The truth is you likely would not even know if you were a carrier. That means we have to protect others from ourselves, by wearing masks when we are in public.

No exceptions.

So at this point – you are hopefully saying “OK you’ve convinced me to make a mask” and are starting to look through your home for material you can use for it.

The interview with Matteo below will explain:

  • How we can test fabric we have around at home to determine if it is usable or not.
  • How well DIY masks with household fabric work at:
    • protecting others from our germs (since we can all be carriers)
    • protecting us from others’ germs (when we have to enter a potentially infected public area)

LR: Hi Matteo! Thanks for helping me understand how to do this right.

MB: My pleasure.

LR: The first point we should make is that – even after making a mask using material that passes the tests we explain below – we are still making masks that are primarily for keeping us from infecting others – and they are less effective at protecting us from actual small droplets containing the virus. However if we all wear these masks, then we can be more successful at protecting each other.

MB: Yes. So the problem we are trying to solve is that COVID-19 transmits through the air via water droplets. So, let’s say you are infected. When you breathe out – that’s right – just by breathing out – regardless of whether you are actually coughing or sneezing into the air – you are omitting droplets that could contain the virus.

The size of the droplets is randomized. It could be a bunch of little droplets or it could be a few big droplets. Now the bigger droplets, containing more of the virus, are going to drop down to the ground, because of gravity, while the little ones are going to stay in the air longer. (Just like the difference between when you throw a feather or throw a stone.)

This is why you need to stay at least six feet away from everyone when you are out in public, and it’s also why these falling droplets – both small and large – will all fall on all surfaces and the floor (called “fomites“) as you are walking around in public. (And yes, the virus particles on the floor can live on the bottom of your shoes for a couple days. So, it’s important to leave your shoes at the door when you come home and never walk around in your house with your outside shoes on.)

If you’re standing close to somebody that isn’t wearing a mask, and you are not wearing a mask, you are basically exposed to ALL of their droplets: the big ones AND the little ones. This is why everyone should wear at least some kind of mask. The big droplets can’t even escape if the infected person were wearing a mask. Since anyone can be an asymptomatic carrier, it’s all of our responsibility to wear masks when out in public – even if we think we are healthy.

LR: Ok so, 1) everyone should be wearing some kind of mask, no matter what, preferably with multiple layers of fabric (see why below) and then also 2) when in public, always stand 6 feet away from people.

MB: Yes. So this mask – whatever it’s made of – should protect you from the big drops, but things get more complicated when we are trying to assess how effective these DIY masks are at protecting you from the little droplets.

LR: Ok so let’s talk about the little droplets.

MB: So, again. The best way to protect everyone from being exposed to the little droplets is for everyone to wear masks, so that the little droplets that come out naturally just from breathing aren’t released into the air to begin with.

Ideally, you are hoping that these DIY masks, will be able to catch the little droplets that might not fall right away – thus stopping you from inhaling any infected particles.

LR: How well do these DIY masks actually protect us from smaller water droplets that may be in the air when we are out in the world?

MB: Well, depending on how the fabric was woven, there will be gaps in the fabric of different sizes, depending on the size of its weave. Again, any kind of material quadruple layered or more will probably catch all the big droplets, but not necessarily the little ones.

LR: But how can we know the size of the “weave” – the size of the gaps in any given fabric if that information has not been explicitly specified?

MB: You can’t. Unfortunately, to know that for sure, you would have to set up lab tests. It depends on how quickly it was spun.

These kinds of fabric specifications are not something that most clothing manufacturers or grocery bag makers are equipped to provide. The data is just not available generally.

LR: So our fabric could have been spun at any speed at the factory, and there’s no way to know?

MB: Right. There’s no way to know because, usually, nobody wrote that down at the time. For most types of fabric, it is not required that such information be logged at the time. So, it is not logged – as doing so could get expensive.
LR: Ok so that’s why you recommend doubling or quadrupling the layers, right? To help account for the gaps in the fabric?

MB: Yes.

LR: Okay let’s talk about cleaning masks. Is it true that these DIY reusable masks will need to be cleaned after every use, to be used safely?

MB: Yes. You should do it after every time you go out, right away, when you get home. Hopefully this is just once or twice a week; since you shouldn’t be going out more than that.

LR: How do you clean we clean these masks?

MB: You clean your mask by sterilizing it in water at approximately 92 degrees Celsius or 197.6 degrees Fahrenheit.

Bringing water to a boil is the simplest way to get the water hot enough without having to worry about its actual temperature. (Boiling water is 100 C or 212 F – so it more than covers the temperature requirements.) (Note that it’s important to not boil the mask itself – as you don’t want to risk melting the fabric or any coating on the fabric.)

LR: Okay so, although boiling water is hotter than you need to sterilize, boiling the water until it bubbles is the easiest way to see that it is hot enough to sterilize the mask. And because it’s so much hotter than needed, it’s ok that it cools off a bit when you pour the water into a bowl to put the mask in.

MB: Yep. So, once it has reached a boil, pour the water into a bowl, put the mask in the bowl, and leave the mask in the water for 2 or 3 minutes. Then squeeze it out and let it dry out by hanging it up or laying it on top of a clean towel.

LR: Okay so it sounds like you really need two masks. So one can be drying out and you can still have a dry one ready, just in case you need to go out unexpectedly.

MB: Yes. That would be a good idea. I realize that everything I’m telling you might sound a little excessive, but we are erring on the side of caution here, since lives are at stake.

LR: Understood. So let’s say we are convinced and are ready to make our masks. There are numerous patterns for folks to use, but there isn’t a lot of clear simple guidance about what fabrics are best to use.

For instance, the DIY mask article by Janus Rose in VICE about making your own mask mentions explains that grocery bag material might be best to use, as “non-woven fabrics” are recommended – but what the heck are those?

MB: Well, some reusable grocery bags are made with non-woven fabrics, such as polypropylene, but they are rarely marked or labelled to say what they are made out of. Because, unlike clothing, there is no legal requirement to label grocery bags with what they are made with.

LR: So what can we do then?

MB: You can test the fabric out – to see which of the fabrics you have around your house are best use.

Here are some things you can do to test the fabric to see if it would be good to use as a mask.

The first thing you want to do is put a piece of the fabric across your nose and mouth – to see if you can breathe through it comfortably. (If you can’t breathe without trying hard, you’ll be tempted to take it off when it becomes uncomfortable.)

A lot of fabrics that have a waterproof coating of some sort – which can be good for keeping out infected water droplets. But if you can’t breathe through them, all bets are off. And you need to be able to breathe through it easily, or you won’t keep it on; it’s just human nature. If you use anything that is coated on one side, put the coated side facing out, with the (usually) kinda fuzzy side facing in (on the side where your face is).

The second thing to check is to see how it behaves under the faucet. Non-woven fabric, for instance, is very “hydrophobic” in that water will repel off of it instead of being absorbed. So do this test:

  1. Run the water in your sink and hold the fabric tightly underneath the faucet.
  2. If the water is beading up or reflecting or rolling off when it hits, you have your hydrophobic fabric.
  3. If the water is absorbing into the fabric; it’s not hydrophobic.
  4. Even if it is hydrophobic – be it coated or non-woven – it’s only usable when if can still breathe through it when it’s doubled up.

MB: Most fabrics (like cotton or your average clothing fabrics) will just absorb the water, and these are still usable, if that’s all you have. If you use more layers it can still provide a reasonable amount of protection.

LR: So use what you can breathe through that you have around – if you can’t find any of these “hydrophobic” fabrics – but in that case, use lots of layers.

MB: Yes. But you should, at the very least, double it up. And four layers or eight layers is even better. You basically want as many layers as you can while still being able to breathe through it.

LR: Okay so once we have tested the fabric to make sure that we can still breathe through easily when we have 2 layers minimum and 8 layers if possible – and, ideally, is also water repellent.

MB: Yes. And in that case, by the way, have the the waterproof part facing outward – rather than against your face, if possible. (It will be uncomfortable against your face the longer you wear the mask, and you don’t want to get uncomfortable wearing the mask and need to take it off.)

LR: So basically, follow these simple steps :

  • check that you can breathe easily through the fabric you are considering (and make sure you can still breathe through it when it is doubled or quadrupled in thickness.
  • double the fabric at minimum and quadruple it (or more) if possible.
  • even with your mask on, remember to still stay 6 feet away from others, when possible.
  • wash your mask every time you come home.
  • try to have two masks, so you will always have a clean one handy.

MB: Yes. Also, for those of you who are sick – and not sure what they have, but need to leave the house, like to pick up an antibiotic prescription. I have a pattern for a salt filter mask that can help catch droplets and help dehydrate the virus in them when they are caught. It’s based off a paper in Nature.

LR: Great I will include link to that and also for your plastic face shield design that uses 3D printed parts.

Thank you so much Matteo!



  1. Sources for this article
  2. Patterns to use to make masks
  3. About Matteo Borri
Sources for this article
    1. Evaluation of heating and chemical protocols for inactivating SARS-CoV-2 – Boris Pastorino, Franck Touret, Magali Gilles, Xavier de Lamballerie, Remi N. Charrel – BioRxiv – https://www.biorxiv.org/content/10.1101/2020.04.11.036855v1
    2. Use of Cloth Face Coverings to Help Slow the Spread of COVID-19 – CDC – April 7, 2020
    3. Social Distancing, Quarantine, and Isolation – Keep Your Distance to Slow the Spread – CDC – April 7, 2020
    4. Respiratory virus shedding in exhaled breath and efficacy of face masks – Nature Medicine – April 3, 2020 (Nancy H. L. Leung, Daniel K. W. Chu, Eunice Y. C. Shiu, Kwok-Hung Chan, James J. McDevitt, Benien J. P. Hau, Hui-Ling Yen, Yuguo Li, Dennis K. M. Ip, J. S. Malik Peiris, Wing-Hong Seto, Gabriel M. Leung, Donald K. Milton & Benjamin J. Cowling) (PDF) https://www.nature.com/articles/s41591-020-0843-2?fbclid=IwAR36pMg1v4Io4tmiJdMrPvbHAEehgGbE7bemLcKeOxcPGuHHIrhu0e3x52g

    5. Fomite – Wikipedia – https://en.wikipedia.org/wiki/Fomite
    6. We’re Running Out of Face Masks, But You Can Make One Yourself – Amateur crafters are sending improvised masks to the frontlines of the COVID-19 crisis. With a bit of practice, you can make one for yourself. By Janus Rose for VICE – April 1, 2020 – https://www.vice.com/en_us/article/qjd59q/how-to-sew-your-own-face-mask-diy-covid-19
    7. Meet The DIY Ravers Giving Free Masks to Every New Yorker – Masks For The Masses wants everyone in New York City to have a cloth mask—no questions asked. By Janus Rose for VICE – April 8, 2020 – https://www.vice.com/en_us/article/v74k5b/meet-the-diy-ravers-giving-free-masks-to-every-new-yorker
    8. Matteo’s salt filter mask The salt filter will intercept aerosol and droplets coming into your mouth, and neutralize pathogens in them when it recrystallizes https://robots-everywhere.com/re_wiki/pub/web/Cookbook.SaltMask.html

    9. Matteo’s 3D-Printed Face Shield using any Transparent Sheethttps://civilpedia.org/p/?pid=339&t=p&h=3D-Printed

    Patterns you can use to make your own mask
    1. No-Sew Pleated Face Mask with Handkerchief and Hair Tie – Japanese Creations – http://blog.japanesecreations.com/no-sew-face-mask-with-handkerchief-and-hair-tie

    2. How To Sew a Simple Fabric Face Mask – Japanese Creations – https://blog.japanesecreations.com/how-to-sew-a-simple-fabric-face-mask
    3. A pleated pattern for a stand alone mask that came recommended to us – with some tips about making them in larger quantities. – Aaron Swartz Day.org https://www.aaronswartzday.org/diy-covid-19-mask-pattern/
    4. DIY Mask – Face Mask Pattern – 2 Styles – Treasure Sewing Blog https://blog.treasurie.com/diy-mask
    5. Ties and Elastic Alternatives – Treasure Sewing Blog https://blog.treasurie.com/diy-mask/#Ties_and_Elastic_Alternatives


    About Matteo Borri

    Matteo Borri is an engineer and inventor for his own company, Robots Everywhere. He is also a NASA contract engineer.

    Matteo invents and consults on everything from lasers, virtual reality devices & development, 3D printing, solar power panel integration (& effective uses of batteries for storing the solar power you generate), autonomous robots (such as the “ant bot”, autonomous delivery robots, underwater fish robots (and of course, autonomous underwater fish robots :) – and yeah, a lot more.  He is also a co-founder of our Solar Survival Project (of which these COVID-19 materials are a product of) – and is an advisor for our SwartzManning VR Destination.

    1. Matteo’s salt filter mask  The salt filter will intercept aerosol and droplets coming into your mouth, and neutralize pathogens in them when it recrystallizes  https://robots-everywhere.com/re_wiki/pub/web/Cookbook.SaltMask.html

    2. Matteo’s 3D-Printed Face Shield using any Transparent Sheethttps://civilpedia.org/p/?pid=339&t=p&h=3D-Printed

November 11 2023 – 11 am -6:30 pm PST