Why you should wear a mask, how to make masks, and the effectiveness of various mask materials

Since the coronavirus started spreading, I’ve been wearing masks when I go out in public.  I’ve gotten responses ranging from fear to arguments, and even name calling, because the CDC and American authorities have been lying to American people about the effectiveness of masks.  Why?  Because there was a shortage.  That doesn’t mean that I shouldn’t wear my mask to protect my 86 year old mother, who I live with.

Some time in the last 24-48 hours, everybody’s attitudes towards masks shifted suddenly.  Everybody wants a mask, and nobody knows where to get them or how to make them.

There were even masks on the runway at Paris Fashion Week!


Lets start off by answering a simple question I know many of you have, after all the misinformation about masks:  How do we know that masks work?


This web page has a chart of data from a Cambridge University study about how well various home made mask materials do when stopping bacteria particles at the various materials.


Do not use vacuum bags in masks!  They usually contain fiberglass that you can inhale, and then the fiberglass rips up your lungs.  You don’t want lungs full of fiberglass when COVID19 infects you.

The bacteria used in the Cambridge study are between 0.023 and 1.25 microns in size.  Conventional wisdom seems to be that the COIVD19 virus particles are roughly 0.14 microns in size.  Absolutely none of the materials in the Cambridge study have pores tight enough to physically stop all particles that are 0.14 microns.  Even the best N95 masks have pores are something like 0.4 microns in size.  So how can masks be effective?

The pores don’t have to be tight enough to stop a 0.14 micron particle to stop COVID19.  In the air, COVID19 can’t survive outside of water droplets.  So to be effective, a mask just has to stop the water droplets that the COVID19 particles travel in.  Lucky for us, water mist particles are orders of magnitude larger than virus particles.  The droplets in water mist are between 70-350 microns in size (depending on the dew point).  This makes masks more effective than the Cambridge study suggests, but the Cambridge numbers should be considered a baseline.  We know, for example, that a single ply cotton mask will stop at least 70% of COVID19 from getting into your nose and throat.

What good is stopping 70% of them if 30% of the particles can get through and infect you?  Well, it’s all about viral load.  Viral load is how large the volume of virus particles are in your body.  If the viral load is too small, you might not get sick.  It is better to breathe in 1,000 COVID19 virus particles than 1,000,000 COVID19 virus particles, because if the viral load is low enough, your body can fight the invading COVID19 particles much more effectively.  The virus’s effects are directly tied to how large the viral load is in your body.  As the load gets bigger, your symptoms get worse.  If the load is small enough for your body to eliminate it before it grows, you don’t get sick.  That’s why you should wear a mask.


Surgical masks and N95 masks are made of polypropylene.  Why?  Because they are breathable while being fairly water resistant.

The pores in non-woven polypropylene are something like 0.4 microns large, so they aren’t physically stopping virus or bacteria particles.  They resist water by being negatively charged.  The negative charge captures water droplets, while the pores allow you to breathe through the material.  If you can get your hands on some polypropelyne, you can put it in a home made mask, and it will be at least as effective as a surgical mask.

Even with this, they aren’t 100% effective.  N95 masks are 95% effective.  The Cambridge numbers show that surgical masks are 97% effective.

Polypropylene requires special handling to remain effective, though.  The negative charge that protects you breaks down with time and heat.  That’s why N95 masks have expiration dates on them.  Also, if you iron your polypropylene mask, or put it in the laundry machine, you will destroy the negative charge on them, making them much less effective.  Here’s a video demonstrating that.

If you want to reuse masks, you can disinfect them from COVID19 with time or with alcohol.  There are other methods, but alcohol seems to be the best option, if you need to decontaminate them quickly.  Here is a video from a physician, showing how to use alcohol to disinfect surgical masks.  He starts talking about alcohol around the 13:52 mark.  The stuff before that is mythbusters type information that you probably shouldn’t try at home.  Please, don’t fill your house with explosive ozone gas.

Personally, I have 3 surgical masks I wear.  When I get home, I put the mask I was wearing in a box and let it sit for at least 24 hours.  If COVID19 is anything like the other SARS type corona viruses, 24 hours is more than enough time for COVID19 to die on it’s own.  If I have to go out again, I wear a mask that I haven’t worn in at least 24 hours.  If I run out of clean masks (which hasn’t happened yet), I have a cloth mask I can wear, which I line with polypropylene.


As noted above, polypropylene is extremely effective, but you don’t need polypropylene to make an effective mask.  Simple cotton masks are effective at protecting you and those around you.  If you need to make a mask with simple household items, you can make it with a bandanna and two hair ties, as shown in this YouTube video.

I love this design because of it’s simplicity.  It gives you at least 2 layers of cotton, and you can fold another material into the mask to make it more effective.  For example, you can fold a dish rag or a paper towel into it to increase it’s effectiveness.  Also, I’ve seen some materials engineering types say that dried out swiffer wipes make great filters.  If you can get your hands on polypropylene, you can fold that into the bandanna to make it as good as a surgical mask.

EDIT:  Also, you can launder the cloth masks to kill the COVID19 particles.  The soap in the washer, and the heat of the drier kills almost everything, including COVID19.  The heat will destroy polypropylene effectiveness, though, which is why you need to use alcohol with polypropylene.

Where do I get polypropylene?  I ordered polypropylene shoe covers on amazon last week.  They are cheap, they arrived fast, they are highly breathable, and they are the perfect size.  If I fold a shoe cover in half, it fits into my cotton mask perfectly, and it’s 4 ply.  This is the page I ordered them from.  As of this writing, the page I ordered from is out of stock, but if you search around, you can find other polypropylene products that may be usable in masks.  As far as I know, hospitals have no shortage of surgical shoe covers.  If they do, they aren’t requesting help with that situation (see links below for what they are asking for help with), so I don’t think my little box of shoe covers is hurting any medical professionals.

RilexAwhile 100PCS Disposable Boot Shoe Covers Thick Non Woven Polypropylene Durable Anti Static Foot Cover for Medical Construction Workplace Indoor Carpet Floor Protection One Size Fits Most Amazon.com

If you sew, and want to make more fancy masks, this is a great design for that.  The only thing it seems to lack is a nose wire to make it sit on the nose better.  You can just wind a couple of pipe cleaners together or use a straightened out paperclip, sewn into a seam across the nose to get that.  The nose wire really does help prevent it from sliding down your face, and it helps prevent the mask from fogging up your glasses.


So now you have your mask.  It’s made of good materials, and you wear it every time you go out.  What about the hospitals?  They have a mask shortage.  Lets help them out, too…

To start with, you need to check some web sites and facebook groups for the most up to date information on mask donations, because this is a rapidly developing field.  Different hospitals have different requirements for masks, if they take mask donations at all.

Your first stop should be my friend Lishan’s blog post about the COVID19 DIY movement.  This page is like a central hub for all things COVID19 DIY.  Bookmark it, and refer to it when you need information.

Then, go to the Open Source COVID19 Medical Supplies Facebook group and join it.  This is a massive, international group.  It is full of engineers, medical professionals, 3D printer enthusiasts, and craftsy people.  These people sewing making masks, printing face shields, and even sewing hospital gowns to donate.  Some people are making ventilator parts and positive pressure medical masks (which are powered masks that look like the masks worn in Avatar).  This group has been on the forefront of the global COVID19 DIY community since the beginning.  It is not uncommon to see posts in Portugese, Spanish, Italian, and even Japanese.  Just read what you can, and use google translate if it seems like important information is not in your native tongue.  These people will give you all the advice and guidance you need.  Check their organizing documents in the about section to get up to speed fast.

Get Us PPE is a web site that shows you what hospitals need what PPE, and gives you information on their standards.  Some hospitals have lose requirements.  I’ve seen threads on facebook where nurses in New York City are scrambling to get their hands on simple single layer cotton masks.  Others have stricter requirements.  Check what the hospital you plan to donate requires before you spend a weekend making masks for them.

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