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Research and Innovation

N95s, KN95s, KF94s – Oh My! What They Are, How to Choose and Other Questions

Mask testing set-up at the NC State Textile Protection and Comfort Center.
Researchers at the NC State Textile Protection and Comfort Center can test mask performance. Credit: Chandler Probert.

As the new, highly infectious Omicron variant sweeps the nation and the world, public health officials have updated their guidance for masks and respirators.

The Abstract spoke to Bryan Ormond, assistant professor of textile engineering, chemistry and science at North Carolina State University and the Textile Protection and Comfort Center, about the difference between N95s, KN95s and KF94 respirators, what to think about when trying to choose between them, and what you can do if you can’t find one.

The Abstract: Why are people talking about N95 masks now? 

Bryan Ormond: The Omicron variant is extremely transmissible; that’s why people are talking about needing higher levels of mask performance. In some ways, nothing has actually changed in the guidelines or science; if your goal has been to provide yourself with the highest level of respiratory protection available, the filtering facepiece respirators (FFRs) like the N95 have always been the recommended option. However, when everything started in 2020, we did not have the supply of these disposable respirators for the entire population to have steady access, and therefore, the recommendations were to reserve them for the people who needed respirator protection the most – the health care workers, the immunocompromised, the sick. 

Since then, the supply chain for high performance FFRs has caught up. I recently went to a home improvement store and saw N95s on the shelf for the first time since March 2020. And we don’t just have one version of the N95s; we also have KN95s and other products that are similar in performance. 

TA: What are the differences between N95, KN95, and KF94 masks?

Ormond: The biggest difference in these is that they are tested and regulated by different countries. The N95 is the version that has been tested and evaluated to U.S. standards set by NIOSH, or the National Institute for Occupational Safety and Health. The KN95 is the version that meets the Chinese standard. The KF94 is regulated by South Korea’s Ministry of Food and Drug Safety. 

These are all FFRs that provide the higher-end performance regarding respiratory protection for the wearer, but they also are very effective at limiting the spread of infectious particles. While they are all FFRs, it’s important to realize that N95s, KN95s and KF94s are not automatically equivalent. You do see some regulatory differences as well as design differences. 

Both the N95 and the KF94 follow a rigorous test standard accompanied by a strong regulatory body overseeing their production. The KN95s have a similar test standard and performance requirements, but do not have the same level of regulatory oversight during production. 

These are going to be in the upper 90s in terms of the percentage of particles that they filter from the air you breathe, but they can vary significantly in terms of how difficult they are to breathe through. From a protection perspective, the ideal scenario is that everybody could have access to at least an N95. But at the end of the day, while the N95s and other respirators give you the most protection, the best mask is still the one you’re going to wear consistently.

TA: How do they work? 

Ormond: These FFRs are typically going to be made of some sort of nonwoven filtration media. A nonwoven material can be thought of as a mat of fibers melted together. You don’t get the same large holes or gaps between fibers or yarns in nonwovens that you see in woven or knit fabrics.

In terms of how they work, first there is the bulk filtration, where you’re just capturing large things. The particles run into the fiber and are caught. In addition to this mechanical filtration, they also have electrostatic filtration. That means they have an electric charge that helps them capture smaller particles. That charge can wear out over time, which could decrease the overall filtration of the material. 

TA: What factors should you consider when choosing between them? 

Ormond: When you take and test these on a face, the fit will be different. N95s may not fit everybody’s face. When we test N95s on our manikin head form, the head form is a little narrow for it. We don’t always get 95%. Also, they are much more stiff. They don’t conform as well. If you have a smaller face, you might get gaps and it might not work as well for you. So depending on your face shape, you could look at a KF94 or KN95. You’re just trying to get one that fits you better.

TA: How can you tell if a mask is fake?

Ormond: People talk about counterfeit N95s or KN95s; it may not be that they don’t work or that they are knockoffs, it may just be that somebody didn’t pay to have them go through the certification process and is claiming that they are certified. There could be some that are made with materials that are not very good, so you have to be careful. 

If you want to check to see if your respirator has been identified as counterfeit, you can check the CDC’s website that tracks the products that they have taken action on. If you want to check on the performance of a surgical or cloth mask, you can go to this website to see if your product has been submitted to meet the new standard for face coverings from ASTM International. The purpose of this list is to show the relative performance of products that have all been tested under the same conditions. It will tell you the amount of particle filtration and breathability of various products. 

TA: Is it still not OK to have an exhaust valve on your N95?

Ormond: When we tell people not to wear an N95 with an exhaust valve it’s because it’s an airborne infectious disease. If you’re breathing out with it, you’re spreading it, but protecting yourself. 

TA: How should people be cleaning N95s and other masks, and how long can we wear them before they need to be discarded or washed? 

Ormond: For N95s or KN95s, I wouldn’t toss them in the washing machine. There’s a chance you could lose the electrostatic properties as well as damage the materials. For the general public, I would use them for about a week and get another one. If the supply chain has caught up to where we think it has, then that’s the benefit of these. If you have access to them and your goal is to protect yourself as much as possible, they’re disposable, so get another one. 

TA: What if you don’t have a KN95 or N95? What are some tips to increase the safety of our face coverings? 

Ormond: The most important thing with anything you wear is it has to fit your face. An N95 could give you 95 to 100% particle filtration, but if it doesn’t fit your face, that’s going to drop. If you want to go with the FFR like a KN95 or N95, you should try some different ones to make sure they fit. 

While they are not respiratory protection devices, surgical masks can still work really well. In our testing, we’ve found they can get between 40 to 70% in terms of respiratory protection. There are a ton of brackets you can buy for them to help them conform to your face. If you close down the sides, it’s going to be harder to breathe through, but it will be filtering more. 

If all you have is a surgical mask, and you don’t have access to the brackets, you can double-mask using a second cloth mask. The whole point of double masking is to make surgical masks fit better. That’s going to get you a more optional performance in terms of protection.

It comes down to what you’re able to do. If people can take one thing away from this it should be to make sure what you’re wearing fits. 

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