COVID-19, And A Simple, Homemade Respiratory Mask, Part Two ©

 

A do-it-yourself face mask, made with a vacuum cleaner filter bag and a gas mask, as a joke, photograph by the author.

There are a lot of different articles on the web these days, which write about how to make your own COVID-19 face mask (an example is found HERE), but I would rather use peer-reviewed study whenever I can.  So, for information from a Cambridge University study, titled “Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?”, read on – Author’s note.

It has been widely reported in the media that you can make a do-it-yourself COVID-19 face mask from a vacuum cleaner filter bag.  But what is the best household material to make a DIY face mask out of?

 

A do-it-yourself face mask, made with a vacuum cleaner filter bag and a gas mask, as a joke, photograph by the author.

Hmmm...That got me to thinking.  I even had visions of putting a vacuum cleaner filter bag onto the hose end of the Russian gas mask that I bought last year for Halloween.  Now, I never trust what I read in the news, without checking it out first, and so, I did what I always do, and I did some research.

I found and read the 2013, Cambridge University study, “Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?” which wrote about using vacuum cleaner filter bags to make face masks (to read the study go HERE, and for a very good summary of the study, read “What Are The Best Materials for Making DIY Masks”, HERE).

But, before we get into the nitty-gritty of what is the best household material to make a DIY face mask out of, let’s talk about what face masks are supposed to do.

A commercially made surgical mask and a commercially made N95 mask, photograph by the author.

Face masks such as commercially made surgical masks or commercially made N95 masks¹, reduce your exposure to airborne contaminants by sealing off your mouth and nose from the free flow of outside, contaminated air and by filtering the outside air before you breathe it in.  Face masks can’t prevent infection, they can only reduce your chance of becoming infected.  Also, if you are already ill, they will reduce the chance that you could spread your illness to others, by the respiratory droplets you produce when coughing, sneezing and talking.  Also, no matter how efficient a face mask is at filtering out contaminants, if you don’t practice good preventative measures, like regular handwashing, not touching your face and eyes and social isolation; it will not reduce your chances of becoming sick.

 

An excerpt from “Testing the Efficacy of Homemade Masks”, page 416

So, what did the authors of the 2013, Cambridge University study, titled “Testing the Efficacy of Homemade Masks” find when they tested common household items, including vacuum cleaner filter bags?  What is the best household material to make a DIY face mask out?

According to the authors, Davies et al., breathability is as important a consideration in face mask design, as filtering efficiency.  This is because, if the material that your mask is made of is difficult to breathe through, then your mask will be less comfortable to wear and if it is not comfortable to wear, then that will influence how long you will wear the mask.

So, let's look at the household items that were tested and see how they stack up on both breathability and filter efficiency, when compared to a commercially made surgical mask.  The authors of “Testing the Efficacy of Homemade Masks” tested the following, a 100% cotton T-shirt, a scarf, a tea-towel², a pillowcase, an antimicrobial pillowcase, a surgical mask, cotton blend cloth, linen, silk and of course, vacuum cleaner filter bags.

  

The authors of “Testing the Efficacy of Homemade Masks”, tested these household items against Bacillus atrophaeus, a rod-shaped bacterium, that is .95 to 1.25 µ (micron) and against Bacteriphage MS2, which is .023 µ (micron). 

 

An excerpt from “What Are The Best Materials for Making DIY Masks?”, March 3, 2020, by Paddy Robertson.

When the researchers tested these various household items against the .95 to 1.25 µ (micron) sized Bacillus atrophaeus, they found that the vacuum cleaner filter bag was 94% efficient at blocking these .95 to 1.25 µ (micron) sized particles, the tea-towel was 83% efficient, cotton mix or blend cloth was 75% efficient, 100% cotton T-shirt was 69% efficient, followed by an antimicrobial pillow case at 66%, a scarf at 62%, a normal pillowcase at 61%, and with all other fabrics being between 60% and 58% efficient.  By using two layers of tea-towel material, two layers of 100% cotton T-shirt or two layers of normal pillowcase material, the researchers found that filtering efficiency increased to 97% for the tea-towel cloth, 71% for the 100% cotton T-shirt material and 62% for the pillowcase cloth.  As a comparison, when tested, a commercially produced surgical mask filtered out 96% of the .95 to 1.25 µ (micron) sized particles of Bacillus atrophaeus in the atmosphere.

 

] An excerpt from “What Are The Best Materials for Making DIY Masks?”, March 3, 2020, by Paddy Robertson.

Since the COVID-19 virus particle is only .1 µ (micron) in size, the crucial test, in light of the current worldwide pandemic, is the test the researchers performed using Bacteriphage MS2, which at .023 µ (micron) is smaller than the COVID-19 virus particle.  When this test was performed the researchers found that the vacuum cleaner filter bag was 86% efficient at blocking the .023 µ (micron) sized particles, the tea-towel was 72% efficient, cotton mix or blend cloth was 70% efficient, an antimicrobial pillow case at 69%, a normal pillowcase at 57%, a 100% cotton T-shirt was 51% efficient, followed by a scarf at 49%, and with all other fabrics being between 62% to 54% efficient.  In contrast, a commercially produced surgical mask filtered out 90% of the .023 µ (micron) sized Bacteriphage MS2 particles from the atmosphere.

So, what does all this mean.  If you are only measuring filtering efficiency, then you would want to make your mask from two layers of tea-towel material, or from vacuum cleaner filter bag, since these had the highest filtering efficiencies in both tests and were equivalent to a commercially made surgical mask, with regards to filtering efficiency.  However, filtering efficiency isn’t the only consideration when designing a face mask, just as important is breathability.

The authors of “Testing the Efficacy of Homemade Masks” felt the comfort and breathability of the DIY mask was just as important factor as filtering efficiency, since you will not wear a mask that is difficult to breathe in or uncomfortable to wear, for very long.  If the mask you are wearing is difficult to breathe in, you will have to work harder to get enough air, this is particularly a problem if you are doing heavy labor or have an underlying breathing difficulty.  Additionally, a mask which is difficult to breathe in may suffer from air leaks around the edges of the mask, as the wearer struggles to draw in enough air.

 

Based on data from “Testing the Efficacy of Homemade Masks”, Davies et al., graph by the author.

To determine how breathable ordinary household materials were, Davies, et al., measured the pressure drop across the materials, noting on page 417 of “Testing the Efficacy of Homemade Masks”, that the pressure drop across a mask would be, “a useful measure both of resistance to breathing and the potential for bypass of air around the filter seal”. 

What the authors found, is that the vacuum cleaner filter bag and the two layers of tea-towels, while the best at filtering, were the worst when it came to breathability.  The two household materials that came the closest to the breathability of a commercially made surgical mask, were two layers of 100% cotton T-shirt and two layers of normal pillowcase material. 

 

Don’t use a vacuum cleaner filter bag to make a do-it-yourself face mask, according to the authors of “Testing the Efficacy of Homemade Masks”, photograph by the author.

According to the authors, Davies et al, the answer to can you make a face mask from a vacuum cleaner filter bag, is yes, yes you can make a do-it-yourself COVID-19 face mask from a vacuum cleaner filter bag, but you wouldn’t want to, because a vacuum cleaner bag is stiff, there might be issues with fitting it properly and even more importantly a vacuum cleaner filter bag is not easy to breathe through!  And while the vacuum cleaner filter bag and two layers of tea-towels made the best filters, they were the worst when it came to breathability, and therefore the authors concluded, they should not be used to make face masks.  Instead, they found, that you should use two layers of 100% cotton T-shirt material or, as a second best, two layers of pillowcase cloth to make your do-it-yourself face mask, as these would be the most comfortable for long term wear, have the best breathability, and at 71% filter efficiency for two layers of 100% cotton T-shirt material and 62% efficiency for two layers of normal pillowcase cloth, when tested against the .95 to 1.25 µ (micron) sized Bacillus atrophaeus particles, still remove a high level of contaminants.  These two materials when tested against Bacteriphage MS2, which at .023 µ (micron) is smaller than the COVID-19 virus particle, had for a 100% cotton T-shirt material, a 51% filter efficiency and for normal pillowcase cloth, a 57% efficiency.

For instructions on how to make a do-it-yourself, homemade face mask, according to the study a "Simple Respiratory Mask" read “COVID-19, And A Simple, Homemade Respiratory Mask ©”, found HERE.  And for a video demonstrating how to put on the mask built according to the study a "Simple Respiratory Mask", go HERE or HERE.

I hope that you continue to enjoy The Woodsman’s Journal Online and look for me on YouTube at Bandanaman Productions for other related videos, HERE.  Don’t forget to follow me on both The Woodsman’s Journal Online, HERE, and subscribe to BandanaMan Productions on YouTube.  If you have questions, as always, feel free to leave a comment on either site.  I announce new articles on Facebook at Eric Reynolds, on Instagram at bandanamanaproductions, and on VK at Eric Reynolds, so watch for me.

That is all for now, and as always, until next time, Happy Trails!

Notes

¹ For my European readers, a United States N95 respirator is the equivalent of a Filtering Facepiece against Particles (FFP)-2 mask.

² A British tea-towel is made of a strong fabric with a thick weave and is called a kitchen towel or a dish cloth in the United States.

Sources

Achenbach, Joel, Sun, Lena H., and McGinley, Laurie; The Washington Post, March 30, 2020 “CDC considering recommending general public wear face coverings in public”, https://www.washingtonpost.com/health/cdc-considering-recommending-general-public-wear-face-coverings-in-public/2020/03/30/6a3e495c-7280-11ea-87da-77a8136c1a6d_story.html, accessed April 3, 2020

Davies, Anna, BSc, Thompson, Katy-Anne, BSc, Giri, Karthika, BSc, Kafatos, George, MSc. Walker, Jimmy, PhD, and Bennett, Allan, BSc; “Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?”, Disaster Medicine and Public Health Preparedness, Vol. 7, No. 4, April 9, 2013, [Society for Disaster Medicine and Public Health, Inc., Cambridge University], page 413-418, https://www.cambridge.org/core/services/aop-cambridge-core/content/view/0921A05A69A9419C862FA2F35F819D55/S1935789313000438a.pdf/testing_the_efficacy_of_homemade_masks_would_they_protect_in_an_influenza_pandemic.pdf, accessed April 3, 2020

Robertson, Paddy; “What Are The Best Materials for Making DIY Masks?”, March 3, 2020, https://smartairfilters.com/en/blog/best-materials-make-diy-face-mask-virus/, accessed April 6, 2020

Robertson, Paddy; “Can DIY Masks Protect Us from Coronavirus?” March 3, 2020, https://smartairfilters.com/en/blog/diy-homemade-mask-protect-virus-coronavirus/, accessed April 6, 2020

Simpson, Leah; “Trump says N95 mask makers 3M 'will have a big price to pay' for selling to higher bidding foreign countries as he invokes Defense Production Act and forces the firm to supply to the US”, Dailymail.com, April 3, 2020, https://www.dailymail.co.uk/news/article-8183153/Trump-says-N95-mask-makers-3M-big-price-pay-selling-higher-bidding-countries.html, accessed April 3, 2020