➡️ I'm seeing a lot of "N95s work and other masks do not"

➡️ Filtration is relative, not absolute

➡️ Summary and infographic ⬇️

⬇️%s are filtration percentages for submicron (less than 1 micron) particles - aerosol data - the relevant size because

90% N95s without fit testing
70% Level 1 medical with cotton overmask
50% Level 1 medical or well-fitting 2-layer cotton

What does it mean?

➡️ Wear the best mask available

If you have access to N95s or FFP3s with overhead elastic, wear them

Otherwise use what you have: any mask is better than no mask

A certified medical mask with a good-fitting cloth mask over the top to improve the edge seal is a great low-cost combo

Mask braces are a bit uncomfortable but is you are in a high-risk situation (eg health care worker not supplied with routine N95s) they greatly improve the filtration of medical masks

@cmclase I think in terms of "inhalation dose" which part of the picture, the rest being how receptive a given vector is -- temperature of nasal passages, for example, and humidity, and so on. I lower dose with the open window and the Corsi box, and in public with the N95.


Never ever wear a cloth mask or a KN95 mask, they are not reliable at preventing infection.

N95 respirators are easier to breathe through than a cloth mask. They are available for free from most pharmacies, just ask.

An N100 / P100 elastomeric respirator has the highest efficiency at a reasonable price and they are easier to perform a seal check on. They are available from any PPE vendor or even from many hardware stores.

@Pat I totally agree with your approach. Encourage elastomerics, N95s, FFP3s.

But when you say not to wear anything else:

➡️ people without access to these are disempowered

➡️ we downplay the contributions of mask-making volunteer groups early in the pandemic and may even create confusion about whether those early masks worked (they did)

➡️ the absoluteness is not in keeping with the peer-reviewed evidence which we summarize here⬇️

Also it makes it seem like we disagree, which I doubt!

We also curate curated lists of ⬇️

✨ We would welcome additions to this page from outside North America✨

Thanks for the interest!❤️


Summary: If you don't want to die, wear an N95 or better. Otherwise wear a cloth mask.

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