Why your choice of fabric for face masks makes a difference

There is much confusion about the efficacy of facemasks; and what fabric is the best choice for masks. 

Masks work in two ways: the fabric  filters (stops) the particles and the seal between the mask and the face also keeps  the virus from getting to your nose or mouth, direct routes to your respiratory tract. Please also keep in mind that, although most people instantly think that masks are primarily worn to protect the mask wearer; in controlling the Covid-19 pandemic, an equally important role for masks has been to protect others from the mask wearer.  Many people are suspected to be asymptomatic carriers, sick with the disease but unaware because they have no symptoms.

Masks turn out to be from good to very good protection, even loose-fitting ones made of any fabric, but let’s look at the debate and the evidence.  Then we can look at some of the good, better, best fabric claims and offer our recommendations. 

Confusion about mask efficacy  is in part due to the fact that there is little agreement how the coronavirus gets from an infected person to you. This is the “droplet versus aerosol” debate.

To understand that debate, we must first look at how small the coronavirus is.

The brown large object is one human hair, about 100 microns (one micron is one tenth of one Millimeter).  The red thing is a red blood cell, about .007 micron and the little, hard-to-see dot to the right of the red blood cell is the coronavirus, about .0005 micron.

The coronavirus is smaller than microscopic size, meaning that we cannot even see the coronavirus with microscopes.   We have to do fluid tests, usually blood tests.

A closer view in the second picture above reveals the coronavirus, in red, the smallest object in the picture,  next to a bacteria, the oblong shaped object.  Bacteria are much larger than viruses. Bacteria are also alive, and can reproduce without a host. One of the fascinating things about virus is that they are not “alive” but are in a middle state between living and non-living. They need a host to survive.

In getting to that host, if you are a health care worker exposed to COVID19, or if you are in a situation where you know you will be in indoor or enclosed spaces  where air circulation is limited, you will want an N95 mask or equivalent;¹ and you want to pay attention to WHO directions on achieving a proper mask seal, both negative (breathing out) and positive (breathing in).  

The 95 in N95, the US standard, means that 95% of particles of size .3 microns are stopped by the mask in tests.  But we know that the coronavirus is .1 microns, much smaller than the pores in even an N95 mask.  

The reason masks do stop the coronavirus is that the virus particles are not buzzing around solo, but are attached to water droplets. Water droplets are much larger than the holes in most masks:

The transparent big blob in the illustration above is a droplet, which humans produce when they sneeze, cough, sing, even talk. The tiny red bits are the coronavirus which hitch a ride in and on the droplet.

With the major way that the virus gets from an infected person to you being via droplets; even a mask made out of not very tightly woven material that fits OK against your skin is a good bet to be good protection.  The water droplets are also much less likely to be breathed in via migration around a gap in the seal of the mask as a solo, tiny, lightweight virus particle.

So you can achieve a surprising degree of protection by using a mask, any mask.  This is especially true because part of the severity of Covid-19, should you be infected, is the amount of the virus, or the viral load,  that you receive.  So even filtering out 80% or 40% or 20% of the virus is better than  filtering out nothing.

There are other reasons why fabric stops particles,  involving Brownian motion, electrostatic charge, the hydrophilic or hydrophobic nature of the fabric,  and “anti-microbial” characteristics.  What are these factors?

Brownian motion:  You may remember if you took any high school physics. It’s the tendency of molecules not to stay still but to jiggle and constantly gyrate and move around.  The idea is that the virus particles do not take a direct route through fabric pores, but bump into and get destroyed by the fibers around the pores as they gyrate through in a less than straight line route.  That is, if they are aerosolized.

Electrostatic charge:  Think static electricity. Did you ever rub your slippers on the carpet and then touch your sibling to shock them?  Some fabrics like silk and some synthetics (do not use synthetics) maintain a charge and the assumption is that the charge helps kill the virus.

Hydrophilic and hydrophobic fabrics:  Hydrophilic fabrics attract water; hydrophobic repel them. We’ve seen both claimed as virus protectors.

Now, the real world just is not so simple, and some of the coronavirus does appear to be aerosolized. Not all coronavirus stay on and in the droplets.  There appears to be some aerosolization. So that means that, although  masks are a means of decreasing your risk of getting infected,  you still must wear masks in conjunction with social distancing and washing your hands frequently.

Remember that the intended major reason for wearing masks is to protect everybody else near you from you in case you are an asymptomatic carrier.  (This is still the major reason many organizations state – to protect others from asymptomatic carriers.)

The evidence is gathering that masks are good at protecting us all from infected mask wearers.  The statement that masks are good at stopping spread is supported by many recent events, such as the tracing of all of the passengers and crew  on a long airplane flight from China to Canada on January 22, 2020.   There were two infected Chinese people on the flight; but none of the other passengers on the very full flight  contracted the virus.  Researchers attributed this good result primarily to the fact that the two Chinese people were wearing masks the entire flight.  As the scientist wrote of this research, “… the lack of secondary cases after prolonged air travel exposure supports droplet transmission, not airborne, as the likely route of spread of the COVID-19.”²  

What fabric should I use?

There are many studies about good, better, best mask fabric, and they are worth reviewing briefly.

A Cambridge University Press published study reports that most any mask using any fabric is better than nothing; but some fabrics are better protection.³  They judged fabric using the direct shooting of .1MM sized particles at fabric; but they also looked at “fit factor, ” a means of studying the leakage around the edges of the mask.  Fit factor was their method of estimating the combined effects of filtration efficiency and “goodness of fit.”  The barometric pressure drop inside of the fabric and outside of the fabric are part of the equation.

But, despite the fact that some fabrics stop particles better, if those fabrics are not comfortable, don’t use them. A mask does not work if you take it off; and people take masks off if they are uncomfortable – scratchy, hot, or difficult to breathe through. A common complaint elastic rubbing sore spots around the ears.  (Again, don’t use plastic. Use fabric ties.)

From the Cambridge Study:  “Comfort should be an important factor in the material used to make a homemade mask. The pressure drop across a mask is a useful measure both of resistance to breathing and the potential for bypass of air around the filter seal. If respiratory protection is not capable of accommodating the breathing demands of the wearer, then the device will impose an extra breathing load on the wearer, which …may induce leakage owing to the increased negative pressure in the face mask.”

A study in The Netherlands⁴ concluded that improvised masks using tea cloths (the European term for kitchen towels, although the European brands are often flax linen and more closely woven than American chunky cotton kitchen towels) out-performed surgical masks over a three-hour period just because the volunteers were more likely to continue to wear them.

A Wake Forest Baptist Medical Center study used the .1 micron projection method of determining effectiveness as well. They found that that fabric whose weave is so tight that you have to breathe heavily was not a good choice. The heavy breathing becomes uncomfortable and you won’t wear the mask, plus it can induce infiltration around the edges.

The Wake Forest doctors recommend relatively closely woven cotton fabric, thread count 180 (or higher – others recommend up to 500, if breathable); with an inner layer of flannel⁵. And though that study does not address it, we would encourage you to use GOTS or Oeko-Tex 100 certified fabrics. (We’ll address our notions of fabric safety at the end of this blog post.)

The studies generally conclude that it’s more important that the mask is comfortable enough so that you continue wearing it than its particulate stopping rating or its ability to maintain a seal.

But it is useful to look at a graphic of the fabrics they judged.  We borrow this graphic  from Paddy Robertson of Smart Air.

Smart Air concludes that the following are the top five for face mask material. 

Smart Air, which has researched, tested and thought about this issue a lot, recommends the five fabrics above for a combination of breathability and filtration effectiveness.

It’s probably best to use a fabric that stops much of the sunlight when held up to the light, but do not go overboard. A black-out fabric would make an uncomfortable  mask fabric that you most likely would not wear.  

We like the Wake Forest Baptist Medical Center fabric conclusions because we agree that masks made from those fabrics  – a cotton “quilting fabric “combined with cotton flannel – will be comfortable and will fulfill the most important factor in choosing mask fabric and mask construction: comfort. If it is comfortable you will wear it.  “Quilting” fabric is usually 4 to 5 oz cotton sateen, one of the most popular fabrics used for bedlinens (sheeting fabric) or very similar.

And you won’t be tempted to keep adjusting it. Best not to touch your face!!

Here, we think that the Wake Forest recommendation is a good one since the flannel is very soft and will not abrade and become uncomfortable like denim and canvas may (the Smart Air fabric recommendation. But hey, if you have soft denim or canvas, you’re good!). 

Flannel is more hot, so an alternative mask using two layers of a closely woven cotton sateen would be a good alternative to have for hot days.  Sateen is the fabric that many bed sheets and pillowcases are made of.  They are also made of percale, jersey (types of fabric construction). Those are a little less tightly woven, but, here again, if it is what you have, anything is better than nothing.

Sheeting fabric made of linen – very finely woven linen using thin yarns (size n21 or thereabouts), works well.  Linen is a really lovely fabric next to skin:  cool in summer and warm in winter.

How about doubling or tripling the fabric in the mask?

Smart Air concluded from their experiments that doubling fabrics was NOT very effective in increasing filtration effectiveness; but many others, such as Wake Forest,  disagree with this conclusion. Studies which recommend doubling fabric include a University of Chicago study, which concluded that a combination of a cotton fabric and either silk or synthetic chiffon (don’t use synthetic chiffon – see below on Plastics) or another fabric with an electrostatic charge⁶, stops a lot of droplets.  They emphasize that fit is important, and note that large gaps between the face and the mask decrease the efficacy of the mask, by as much as half. Still better than no protection.

FABRIC SAFETY CONSIDERATIONS

AND, PLEASE! Consider fabric safety (safety meaning free from residual chemicals of concern in the fabric). Third Party Certifications are tools to help in our decision making.

When buying facemasks or fabric for sewing your own, be sure to use fabrics and masks that are either GOTS certified (Global Organic Textile Standard) or Oeko-Tex 100 certified.   

Oeko-Tex 100 certification is your assurance that the mask and/or fabric is free from residual chemicals of concern. And of note – The Oeko-Tex organization is offering to test face masks for no licensing charge.  Please ask face mask sellers to get their masks tested.  

GOTS certification (Global Organic Textile Standard) provides assurances throughout the supply chain.

Solids are a safer bet than prints

In America we aren’t used to insisting on these certifications (three sources below), so, if you cannot find them, then, a solid fabric is better than any prints because Phthalates are in the vast majority of textile printing inks. Phthalates are extremely disturbing endocrine disruptors that are potent in a minuscule quantity – one in a billion. Phthalates are the class of 29 chemicals that have recently been banned in children’s toys and other children’s articles in the states of Vermont, Washington and California.   

Check for certifications. When you’re breathing through a face mask, you’ll want to be assured the fabric is safe – meaning that you are not breathing in chemicals of concern. 

On Plastic Fabrics

Due to the severity of the pandemic, and the speed at which we need to respond; masks for medical workers is one of the few uses of synthetic fiber fabric, woven or non-woven, that we would not complain about (for a short time).  

We recommend you use natural fiber fabrics for your mask, and insist that mask producers produce masks using natural fiber fabrics. 

Plastic is forever. It is not just single use plastic that is the problem. We need to stop using plastic.

We have, in this blog (meaning all of our postings since 2007), tried to point out the very unfortunate characteristics about synthetic fabric (polyester, nylon, acrylic, polyurethane, etc., etc., etc.) and recycled synthetic fiber or fabric such as recycled polyester.  More and equally important reasons for stopping the use of this plastic fabric have recently arisen: just search microplastic here on our blog or on the web for a start. We’ll blog about this issue more, shortly.

Cooper infused fabric masks

If you have not already seen copper infused or silver infused fabric for masks, you soon will. They are “anti-microbial,” anti-little buggies.  Please do not buy them. It is not clear if they are better protection in protecting you from coronavirus; but, even if they are, even extremely tiny bits of copper are extremely toxic to fish, crustaceans, and algae, which are 10 to 100 times more sensitive to the toxic effect of copper than are mammals . Excess copper in the soil creates a toxic environment for most micro-organisms such as bacteria. 

Although copper does have documented antimicrobial properties, it is a broad-spectrum antimicrobial – meaning that it kills the good guys as well as the bad. Many studies show that this is not necessarily the best approach to infection control. Kaiser Permanente issued a December 2006 memo with this bottom line: “Review of current scientific literature reveals no evidence that environmental surface finishes or fabrics containing antimicrobials assist in preventing infections.” In fact, their policy now is to prohibit any fabrics with antimicrobial finishes in their hospitals.

A FEW OTHER RANDOM ITEMS ABOUT FACE MASKS

On respirators.  

Respirators are the full-face masks used in many industries, like spray painting to protect wearers from toxic vapors

Almost all respirators have one-way valves. This means that the do a good job of protecting the wearer, but that the one-way valve expels everything. They do not accomplish one of the two major reasons for mask wearing:  protecting others from the wearer – the other advantage of mask wearing is to protect the wearer. The protection of others from asymptomatic carriers is a major reason for mask wearing in controlling the pandemic.

These valves are now being banned in many cities.⁷

Mask Re-Use and Cleaning

Even non-woven masks such as N95s that cannot be washed can be used many times. They do not lose their effectiveness easily with use.  

Non-woven masks actually get more effective at particle stopping over time.  They should not be used once they are too hard to breathe through, not just after one use just because they are “single use” and may be contaminated. They can be soaked with hydrogen peroxide or, if not completely soiled, just left alone for a day and the virus will die. 

Smart Air addresses this issue of lifespan.

SOURCES

Where to buy safe and appropriate facemask material and/or already made masks using same

First a note:  There are a lot of “safe and/or green living blogs that list sources of “sustainable or green” face masks. Very few understand fabric safety issues. You are going to breathe through it for hours.  Get a safe one. Certified natural fiber fabric – certified to GOTS or Oeko-Tex 100.

There are actually quite a few sources of GOTS certified quilting fabric – which is often sateen or equally finely woven – that are prints.  Be sure the final fabric is certified GOTS, not just if organic cotton is used.  You can start with organic cotton, but, if the fabric is produced “conventionally,” that is, not according to the strict guidelines of GOTS, then that final fabric is most likely full of chemicals of concern.  As my sister says, fabric is like applesauce. You can start with organic apples, but if you add red dye #2, preservatives, emulsifiers, etc., you don’t get organic applesauce. 

Facemask fabric

Finished masks

IN SHORT

Comfort + fiber + the appropriate weave + no further harm.

The most important characteristic of your mask and mask fabric is COMFORT so you’ll wear it and keep hands away from face.

Look for natural fibers with a tight weave. A layer of cotton sateen or flax linen sheeting fabric, combined with a layer of cotton flannel for warmer weather;  or  two layers of cotton sateen (180 thread count and above, which is most cotton sateen used for bed linens) for cooler weather are both good combinations. 

And, we would also like to encourage you to prioritize asking for GOTS or Oeko-Tex 100 certified fabrics and masks so that they will do not further harm to you, us and the planet.either GOTS certified (Global Organic Textile Standard) or Oeko-Tex 100 certified fabric and/or masks is best.

Failing finding the certifications, use white or off-white colors, not prints. Do not use a print which is not GOTS or Oeko-Tex 100 certified.

And yet, any mask using any fabric is better than no mask. Let’s stop the spread.

 

 

Footnotes

 ^{1 As 3M, an N95 producer,  states on its webpage, “it is reasonable to consider China KN95, AS/NZ P2, Korea 1st Class, and Japan DS FFRs as “equivalent” to US NIOSH N95 and European FFP2 respirators, for filtering non-oil-based particles such as those resulting.  from wildfires, PM 2.5 air pollution, volcanic eruptions, or bioaerosols.}

^{2 “Lack of COVID-19 transmission on an international flight,” Kevin L. Schwartz, Michelle Murti, Michael Finkelstein, Jerome A. Leis, Alanna Fitzgerald-Husek, Laura Bourns, Hamidah Meghani, Andrea Saunders, Vanessa Allen and Barbara Yaffe; CMAJ April 14, 2020 192 (15) E410; DOI: https://doi.org/10.1503/cmaj.75015}

^{3 https://www.cambridge.org/core/journals/disaster-medicine-and-public-health-preparedness/article/testing-the-efficacy-of-homemade-masks-would-they-protect-in-an-influenza-pandemic/0921A05A69A9419C862FA2F35F819D55  The Cambridge University Press study is much quoted, but it looks only at what material stops virus sized particulates from being exhaled directly through the fabric, too. It is primarily a study of what fabric to use in a mask to stop you from infecting others, should you be a symptom free carrier.} 

^{4 Professional and home-made face masks reduce exposure to respiratory infections among the general population.   van der Sande M, Teunis P, Sabel R.   PLoS One. 2008 Jul 9; 3(7):e2618.}

^{5 Wake Forest Medical Center study https://newsroom.wakehealth.edu/News-Releases/2020/04/Testing-Shows-Type-of-Cloth-Used-in-Homemade-Masks-Makes-a-Difference}

 ^{6 When you rub the fabric, do you create static electricity?}

 ^{7 Fast Company: https://www.msn.com/en-us/health/medical/what-is-a-mask-valve-and-why-are-cities-banning-them/ar-BB13jGNN}

Two Sisters Ecotextiles is our online store offering fabric by the yard.