Cutting to the chase: 3M says the differences are not significant!
As practices struggle to obtain enough PPE to meet their needs, it seems that N95 masks are a lot harder to come by than KN95 masks. So, can we use KN95s for the same purposes? 3M, who holds a US license to manufacture N95 masks says, essentially, Yes. N95 is the US standard for a certain level of TESTING for mask performance. KN95 is the Chinese standard. Korea, Japan and the EU also have their own standards. While some of the tests are different, the performance, in ways which matter for Covid-19, is essentially the same.
According to 3M (my underlining):
Based on this comparison, it is reasonable to consider China KN95, AS/NZ P2 Korea 1st Class, and Japan DS2 FFRs as ‘similar’ 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 (e.g. viruses). However, prior to selecting a respirator, users should consult their local respiratory protection protection regulations and requirements or check with their local public health authorities for selection guidance.
The most significant differences between the masks are:
a) The KN95 designation requires masks to be subjected to a ‘FIT’ test where <= 8% of air can escape around the mask. The N95 designation does not require a fit test.
b) The N95 test includes pressure drop limits, both for inhale and exhale. This means mask wearers might perceive the N95 as having greater ‘breathability’.
Here is the original technical bulletin from 3M, “Comparison of FFP2, KN95, and N95 and Other Filtering Facepiece Respirator Classes”
Thomas Talhelm, Associate Professor of Behavior Science at the University of Chicago Booth School of Business wrote a full article comparing these and other masks. Thomas is the founder of Smart Air, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.
One last concern: CDC has warned that there are a fair number of counterfeit N95 masks circulating – these are cases where unscrupulous manufacturers are not even trying to meet the standards of any of the nations listed. We will address in another post some of the ways to tell if the N95 mask you purchased is legitimate. But if you are concerned with counterfeits and are not completely confident in your supply chain, you might be better off with KN95s for now. Why? Because everyone is trying to find N95s, which makes them more expensive than KN95s. And for the same reason counterfeiters print $100 notes and don’t print $5 notes, they almost certainly target the higher priced N95s with their fakes.