The Ultimate Guide to Homemade Face Masks for Coronavirus
One month ago, we published the first readily available data on the best materials for making face masks. Fast forward and the CDC is now recommending face masks for everybody, spurring a worldwide movement to make homemade masks.
The first data summary (viewed over 4 million times!) was a great start on face mask materials, but the data is incomplete. Over the past several weeks, we’ve been hard at work to cover crucial materials the earlier study left out, as well as guidelines for variables like thread count. From coffee filters and bed sheets, to non-woven polypropylene bags, flannels and blue shop towels, let’s jump into the data.
What New Face Mask Materials Do We Have?
We’ve tested 30 new materials in this round of tests, triple what the Cambridge researchers tested.
We chose materials based on popular demand, using this poll we set up on our crowd-funding page . However, we’re still testing, so if there’s a material you want to know about, let us know! We’ll update this list as we run more tests.
We aimed to mimic the test setup the Cambridge researchers used, which is called a Henderson apparatus . In our setup, a fan on one end blows air and particles through the mask material.
On the other end, a Met One GT-521 laser particle counter measures the number of particles that penetrate the mask material. We tested for larger (1-micron) particles and smaller (0.3-micron) particles. These larger particles are approximately the size of the Ebola virus , and the smaller particles are the size of the smallpox virus . The Covid-19 coronavirus measures 0.06-0.14 microns in size, but 5-10 microns when in droplets.
Full details on the testing method are open source and available in our DIY mask material & fabric testing – supplemental data article.
Results: Ebola-Sized Particles (1.0 microns)
For Ebola-sized particles, the N95 mask, surgical mask and HEPA filter performed best, capturing over 99% of particles 1.0 micron and above. Next up, the HERO coffee filter captured 98%. Paper towels, canvas and denim (10oz) and the bed sheet (100% cotton, 120 thread) also captured more than 90%.
All materials were far better than nothing, with the majority blocking more than 50% of particles. But the four worst-scoring materials were the wool scarf, Neck warmer (100% microfiber polyester), bandana (100% cotton) and light scarf.
Results: Smallpox-Sized Particles (0.3 microns)
For 0.3-micron particles, there was a much wider range in effectiveness. The N95 mask, HEPA filter and surgical mask still did best, all capturing over 75%. However, they consistently captured fewer 0.3 micron particles than 1.0 micron particles.
Among the household materials, the HERO coffee filter came up next in the list, capturing 62%. But only 4 other materials filtered more than 48%: the 40D nylon, CHEMEX coffee filter, and kitchen towel and canvas (1.0-1.2mm thick).
Some materials were only slightly better than nothing. The bandana, neck-warmer, scarves and cleaning cloths and 100% cotton t-shirt (1 layer) all captured less than 10%.
The 100% cotton t-shirt result is worth highlighting, as this material was recommended by the Cambridge researchers. In our tests it captured just 3.4% of 0.3 micron and above particles. This is likely because the cotton t-shirt we tested was lightweight, thin material. Material weight and thickness of the material are important factors for face masks. 2 layers of 100% cotton t-shirt performed slightly better, capturing 15% of 0.3 micron particles.
The three scarves we tested all captured fewer than 10% of smallpox-sized particles. The worst scarf material – a 100% ramie (similar to linen) scarf – filtered just 2.8%. President Trump last week recommended using scarves for face masks, but this data shows that these materials rank among the poorest at capturing virus-sized particles.
Natural Fibers Better Than Synthetics
The data shows that natural fibers (like cotton and paper) generally filtered better than synthetic fibers (polyester and polypropylene). Synthetic fibers tend to be smooth and uniform, whereas natural fibers are rougher and more irregular. The irregularity of natural fibers are likely to make them better at capturing tiny particles through Brownian motion .
© Dr. J. Alba (Polytechnic Univ. of Valencia)
The Best Material for Filtration—But Not For a Mask
Based on this data, it would seem easy to recommend the coffee filter and blue nylon as the best materials for homemade masks. But we will end up recommending the paper towel, denim (10oz), and 120 thread bed sheet.
Why? When Smart Air engineer Paddy put the coffee filter and nylon sheet up to his mouth, he found it almost impossible to breathe through. Breathability is crucial when choosing face mask materials.
How Easy is it to Breathe Through These Materials?
To measure the breathability of each material, we recorded the fan power needed to blow a fixed amount of air through each material. You can think of this as the power your lungs need to blow through the material. Here’s how the data pans out (more plusses denotes easier to breathe):
Material Breathability 3M Disposable Floor Cleaning Cloth ++++++ Velvet Synthetic Fiber ++++++ Quick-dry T-shirt (95% Polyester + 5% Spandex) ++++++ Synthetic Brocade Sheet ++++++ Wool Scarf (100% Merino) ++++++ HEPA Filter ++++++ 100% Cotton T-shirt ++++++ Non-woven Polypropylene Bag ++++++ Bandana (100% Cotton) ++++++ Wool Scarf (100% Cashmere) ++++++ Neckwarmer / Snood (100% Microfiber Polyester) ++++++ Light Scarf (100% Ramie) ++++++ Dusting Cloth ++++++ Canvas (0.4-0.5mm thick) ++++++ Surgical Mask +++++ 100% Cotton T-shirt (2 layers) +++++ Bra Pad (muslin + sponge) ++++ 70D Nylon ++++ Paper Towel For Hand Drying +++ Bed sheet (100% Cotton, 120 thread) +++ Bed sheet (100% Cotton, 80 thread) +++ Denim (10oz, 0.6-0.8mm thick) +++ 3M N95 mask +++ Kitchen Towel +++ CHEMEX Coffee Filter ++ Canvas (0.7-0.8mm thick) ++ 40D Nylon* + HERO Coffee Filter* + Canvas (1.0-1.2mm thick)* +
We compared the breathability of the household materials to the surgical mask. Unfortunately, most materials that were the best at filtering particles were also the most difficult to breathe through. That makes sense. A really dense, thick coffee filter can capture particles well, but it won’t let much air through.
To help with gauging breathability, we also tested the breathability of an N95 respirator. They’re known to be a little more difficult to breathe through than a surgical mask.
The 100% cotton T-shirt (2 layers), bra pad, 70D nylon, paper hand drying towel, cotton bed sheet (120 thread) and denim (10oz) all fell between the breathability of the surgical mask and N95 mask.
Breathability and Filtration: The Best Combos for Facemasks
Balancing breathability and filtration, we recommend the paper towel, denim (10oz), and 100% cotton bed sheets (80-120 thread). The bra pad performed fairly well, filtering 14% of 0.3 micron particles, and 76% of 1.0 microns. It could be used as a more quirky face mask material, although men might be too bashful to strap a bra cup to their face in public!
One material that’s easier to breathe through than a surgical mask, and still performed fairly well at filtering particles was the 0.4-0.5mm thick canvas material. This material even performed better than the 100% cotton t-shirt.
However, if you don’t have thicker fabrics at home, our data shows that 100% Cotton t-shirts, layered up, are also still effective options for homemade masks.
Finding the Best Material: The Poor Man’s Fabric Test
One problem for using this data at home is that materials like T-shirts and bed sheets are different. Some are thicker; some are thinner. How can you be sure the material in your home will perform similar to the ones we tested?
Without a $3,000 laser particle counter , here’s one handy way to estimate this: try your own “Poor man’s Fabric Test” to help you out.
Hold your material up to the light.
See how much light passes through it.
Compare it to this rubric to estimate the effectiveness of your material.
Face Mask Materials: Bottom Line
Materials like coffee filters perform exceptionally well at filtering tiny particles, but they are so difficult to breathe through they aren’t practical for making face masks. Based on a combination of breathability and filtration effectiveness, we recommend denim (10oz), bed sheets (80-120 thread), paper towel, canvas (0.4-0.5mm thick), and shop towel for homemade masks.
A Shout Out to Those Who’ve Helped Support Open-Source Tests
The response we received for our initial article covering the best materials for homemade masks was unprecedented. People from Spain to Vietnam have offered to help and shared their thoughts on the best materials for masks. Joni, a disabled veteran with pulmonary disease, and K. Sue, a 70 year old in Rochester, US who donated to our campaign as her 70 th birthday present, are just a few of the people who’ve supported this project and made this open-data possible!
If you’d like to help support us test more materials, check out our campaign here: https://fundly.com/best-diy-mask-materials
What is 10oz denim anyway?
Denim is typically measured in weight per square ounce. A square yard of 10oz denim would weigh 10oz. Anything under 12oz is considered ‘lightweight’ in the denim trousers range, so you can think of the 10oz denim we tested as being similar to that from lightweight trousers.
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