The Ultimate Guide to Homemade Face Masks – Supplemental Data

Ultimate Face Mask Materials Top 5 fabrics for protecting coronavirus

This article accompanies our Ultimate Guide to Homemade Face Masks for Coronavirus article, and covers our testing method and provides the original data.

WATCH: Smart Air’s Paddy Explain How We Ran These Tests

The Cambridge researchers used a fancy piece of kit called a Henderson apparatus to run their tests. This allows for the controlled generation of microbial aerosols and a close control of flow rate and relative humidity. In our tests, we chose to mimic this testing method as closely as possible, but with some noticeable differences. Here’s our setup:

First off, we used ambient air pollution for our tests. The air we breathe contains thousands of tiny particles, some of which are the same size as viruses. We did this so as not to have to work with any nasty viruses or bacteria. We lined two fans up in series to generate a strong airflow, enough to blow through each material at 0.3m/s. That’s similar to speed of the air when exhaling through your mouth.

At the end of our test tunnel, we placed a 10cm x 10cm specimen of each material on the end of the tube, and adjusted the fan to measure 0.3m/s on our anemometer. For some thick materials, our two-fan setup wasn’t powerful enough to reach this speed. Our results reflect which materials these were.

Thick canvas material fabric for making DIY homemade masks for protecting against covid-19 coronavirus

After setting up the material and the airflow, we then proceeded to use our Met One GT521 laser particle counter to measure the number of particles the materials could capture. Met One is the company that makes the big BAM monitors that most governments use to measure air pollution, so we’re in good hands here.

MetOne GT521

We tested the particle capture effectiveness of each material at capturing 1.0 micron and 0.3 micron particles. The 1.0 micron size mimics the Bacillus atrophaeus bacteria used by the Cambridge researchers (0.93-1.25 microns in size). It’s also a size that can be considered similar in range to coronavirus droplets (5-10µm). 0.3 micron particles are typically considered the most difficult to capture, and so was chosen here as a ‘worst case scenario’. It can give a reasonable estimate for effectiveness of each material at capturing 0.1 micron particles – the size of the coronavirus when not in droplet form.

For each material, downstream air was samples for 30s with and without the test specimen in place, and repeated 3 times. Averaging these values gave us our 0.3 and 1.0 micron capture effectiveness for each material.


Open Data On Best Materials for Covonavirus Face Masks


As part of Smart Air’s open-data policy, we are providing all the data in our experiments available for free for people to download and analyse. The data can be downloaded here:

Ultimate DIY Face Mask Materials for Protecting Against Coronavirus Virus.xlsx

Covid19 coronavirus best masks materials fundraiser

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thank you for this test and for sharing all that valuable information.

This latest test says paper towel is actually a pretty good filter.(96%/47%) or am I mistaken?
However, in your older kitchen paper towel test the results were less favourable (about max. half the filtering capacity).

Am I mixing something up?


Hi All,
what is the device that is under the intake fan (Fan1)?
Is that the means to generate the aerosol particles to feed into the test?

Becky H

I found the article on HuffPost and then came here. I searched the article and your information to find out in your testing if you used just one layer of the material. It looks like you might have, but clarification would be helpful. I made cloth masks in 2 layers, the outer layer out of a sturdy pillowcase and inner lining of bandana material. I also provided the wearer with a brown, cone-shaped coffee filter, cut open, to use as an extra layer inside the mask. My son also gave me a roll of blue shop towels, which I see… Read more »


I love this data! I previously heard that shop towels make for a good DIY mask. Some of the info here says that paper towels are better filters. Is there a brand/type of towel that this applies to? There are numerous options for basic paper towel.

Theresa Capri

To be very transparent and accurate, you need to include what will happen if you don’t have a tight fit around your face. What happens if you have a 1/4 inch gap. It seems to me that would negate any findings you have. Your pumps wouldn’t have a hard time pumping around even a 2 mm gap, I would think.