COVID-19 face masks: How high-filtration masks — like the KN95, N95 and KN94 — differ

Why masks come with different letters and numbers

By Nicole Karlis

Senior Writer

Published January 27, 2021 7:40PM (EST)

N95 and KN95 Face Masks (Getty Images)
N95 and KN95 Face Masks (Getty Images)

You've heard of N95 and KN95 masks — but have you heard of the KF94, and what's the difference between the three? 

There are many high-quality masks on the market with different letters and numbers. Understandably, this can be confusing. However, to decipher their differences and how each one works, one must have an understanding of what the different letters and numbers represent.

"The number on all of those refers to its filtration efficiency, so the percentage of articles that it stops from getting through," said Dr. John Volckens, a professor of Mechanical Engineering at Colorado State University.

A KN95 filters 95 percent of particles, and so does an N95. A KF94 filters 94 percent of particles. The difference between the letters is the government standard certification.

"The N in N95 stands for NIOSH [The National Institute for Occupational Safety and Health], and that's the U.S. standard, and it's an occupational standard," Volckens said. "KN95 is a Chinese standard that is close to the U.S. standard and KF94 is a Korean standard."

"N" is also a NIOSH-rating for masks that are non-resistant to oil.

KF literally stands for "Korean filter." Notably, a study published in 2020 showed that KF94 masks are comparable to the N95 in blocking SARS-CoV-2 particles, and more effective than a surgical mask. However, the study was quite limited as only seven patients with SARS-CoV-2 infection participated in it.

"KF94s seem to be more readily available than the N95, less expensive [generally under $2 each] and easier to use for many people," Sonali Advani, an assistant professor of medicine at Duke University, told NPR. "KF94 is actually intended for public use. In Korea they are often worn by ordinary citizens to filter out dust or pollution."

Volckens explained that N95 masks are only certified by one lab that is part of the Centers for Disease Control and Prevention (CDC), and that is partly why supply can't meet demand right now.

"They're very stringent on who they let become an N95, which is why you don't see a lot of them on the market anymore because they've all been purchased," Volckens said. "The problem with KN95 and KN94s is that there are a lot of imposters on the market, and we don't know what you're buying."

When it comes to N95 masks, each mask has a stamp that states it was certified by NIOSH with a certification number that you can look up online. Volckens added there are also masks that have ASTM [American Society for Testing and Materials] standards that are "nearly equivalent" to N95 masks— like the FFP2, which stands for "filtering face-piece two level" mask.

In some parts of Europe, like Germany, the federal and state governments are mandating that FFP2 masks are used in stores and on public transportation now. According to NPR, Austria is making similar recommendations. In France, the High Council for Public Health announced it is also recommending people wear surgical masks in public— instead of fabric masks.

In the U.S., the CDC continues to recommend fabric masks for the general public, as long as they have at least two layers.

Volckens said if you're buying a fabric mask, you should look for three key characteristics: fit, filtration and breathability.

"Filtration ability of the fabric, you want a highly-effective filter, you want a fit — and that's a personal thing, but you want to get the mask to fit closely all across your face, and then breathability, you have to be able to breathe through the mask normally," Volckens said. "Otherwise, if it's uncomfortable to breathe through you're not going to wear it, and it could be unsafe."

Of course, it's difficult to know the fit of a mask until it's purchased. But Volckens said people should buy masks from a supplier that has been filter tested. Regarding the fit of the mask, that can be reconciled by double masking.

"That's why you can double mask because you can buy a mask that doesn't fit well but then use something else to hold that mask closer to your face," Volckens said. "That's what we talk about double masking being effective on fit."

By Nicole Karlis

Nicole Karlis is a senior writer at Salon, specializing in health and science. Tweet her @nicolekarlis.

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