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The university of Hong Kong-Shenzhen Hospital said homemade mask, made using 2 kitchen and 1 tissue paper, achieved 90% of the filtering function of surgical masks.

That's a very good approximation to an original surgical mask.

Why the CDC is not recommending this type of masks?

Why is recommending cotton face masks instead?

Thank you.

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    What is the purpose of a mask? Not a respirator -- a mask? Once you've answered that, you have to be asking yourself how much its filtration efficiency matters. – Carey Gregory Jun 9 at 23:29
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    @CareyGregory The purpose of the mask is to protect others from the wearer, in case that they have COVID-19. The problem is that in some places not all people are wearing masks, not all are respecting the social distancing, etc. so how one is supposed to be protected from them? Clearly the cotton mask won't work as expected thanks to this people that for some reason are like if nothing is happening. – I likeThatMeow Jun 10 at 1:07
  • Breathability matters. Kitchen towels are hard to breathe through (I have some of that fabric.) Breathing through two layers would be exceedingly difficult for more than a few minutes, let alone with yet another added layer. – anongoodnurse Jun 10 at 19:15
  • @anongoodnurse I see. Is the kind of difficult that could produce headaches? – I likeThatMeow Jun 10 at 21:22
  • More likely that mask would just be taken off. I know I can't wear a 3-layer mask with even only one layer of kitchen towel. – anongoodnurse Jun 11 at 13:51
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This is an early paper on the efficiency of different fabrics for virus filtration. (Lots of testing as gone on since then.) However, it nicely illustrates breathability, the other factor to consider when making a mask:

enter image description here

They summarize nicely here:

Although the dish towel and the vacuum bag captured the most particles, they were also the hardest to breath through. With two layers, the dish towel was over twice as hard to breathe through as the surgical mask.

If you can't breathe trough it, you won't wear it for any significant length of time, making it useless as a mask.

I don't agree with the conclusions; as I said, a lot of research has been done since then. But it has a nice illustration of breathability, and why it matters.

Why is recommending cotton face masks instead?

Although this paper doesn't answer the question specifically (as they jumped from cotton jersey to tightly woven pillowcases, the answer is it has decent filtration plus decent breathability, i.e. it is somewhat effective, and it will be worn.

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