Let’s get the data out there:
A cotton mask provides between 60-70% of the protection of a hospital, disposable mask. A single layer cotton mask catches about 50% of .2-1 micron droplets and particles, and most of 5-10 micron particles, which is significantly more than catching none because you’re barefaced.
There’s a big hole in the disposable mask supply chain right now, but case transmission will increase while we’re waiting for shipments. Thus, some protection is better than none, and protection that can be cleaned and reused is better than continuing to use masks that now themselves harbor a major quantity of germs, both viral and bacterial.
A cotton mask also slows *transmission* because the mask catches a person’s cough, so there’s less aerosolized goop being pushed into the air. Most of the aerosolized transmission of viruses between people comes when someone coughs; those droplets are usually around 5-10 microns (because the virus comes out of our throats coated in spit and crud, not by itself).
A couple layers of cotton does catch spit particles as they leave our mouths. On that side, a cotton mask is a wearable handkerchief, and that’s a good thing, because elbow coughing practice is imperfect.
And since the data is starting to show that we have a lot of asymptomatic/covert carriers in the population, making a 2-4 layer cotton mask part of everyone’s regular kit means reducing the transmission rates when we must interact.
DIY fabric masks can also be built to accommodate PM2.5 (2.5 micron particulates) inserts. These inserts are effective filters, and if they’re inside a washable, changeable fabric mask, they stay effective longer.
Ideally, yes, we’d be using disposable hospital masks and well fitted respirators. We left ideal about 4 weeks behind us.
We need to preserve the remaining stock of disposables for actual sterile conditions, while still trying to lower the rate of transmission. It’s better to send a patient home with 3 cloth masks they can wear to protect those around them than to send them with nothing.
Cloth masks are considered a last resort, and yes, we are at the Last Resort.
If you don’t want to make masks, then don’t. But don’t get complacent.
The CDC is telling hospitals to use bandanas because we’re in Crisis Capacity now. And we can do better than that.
What’s the worst case? We use up stash, get that stash onto people’s faces so the disposable masks can be preserved for times when there is no substitute. It’s stash — it’s not like we were using it for anything anyway.