First-Ever Published Study Reveals How Poorly KN95 Masks Fit, Seal and Protect vs. a Leading N95 Respirator

With fit and seal being vital for mask effectiveness, testing by Shawmut Corp. revealed NIOSH-approved N95s offered up to 70 times better protection

West Bridgewater, MA (January 24, 2022) – NIOSH-approved N95 filtering facepiece respirators may provide as much as 70 times better protection compared with Chinese-standard KN95 masks, according to study data released today by Shawmut Corp. The company completed a study using the ASTM Respirator Fit Capability standard to compare how well 95% filtration KN95 masks fit and seal against air leakage, which is essential for effective protection.

“These results are very concerning,” Shawmut CEO James Wyner said. “With so many people promoting the use of KN95 masks, we thought it was important to measure their fit. It turns out KN95 masks fit so poorly on most people that the high-quality 95% filter doesn’t fully perform its function. The idea that a properly vetted KN95 is any way comparable to an N95 is categorically wrong and dangerous, especially with a SARS-CoV-2 variant as infectious as Omicron. We felt it was critical to get the information out to the public.”

When tested side-by-side with a high-quality N95 mask, the KN95 masks exposed wearers to 25 to 70 times the level of small airborne particles relative to the N95 control, according to the study. In 12% of the cases, measurements indicated the KN95 offered no protection at all, with 100% leakage around the edges. In nearly half (47%), the wearer had at least 33% leakage around the edges. The N95, meanwhile, averaged far less than 1% leakage.

The study comprised 800 individual measurements of the Shawmut Protex SR9520 Respirator (M/L size) and three high-quality KN95 respirators on a 25-person panel selected in accordance with the NIOSH bivariate test panel, which is designed to be representative of the U.S. civilian workforce. The testing found that the KN95 masks in the study, which achieved at least 95% filtration on tests similar to those used by NIOSH for U.S. respirator certification, demonstrated a tremendous amount of leakage. The net result is that much of the airflow in the KN95 design is around the edges of the facepiece, not through the filter.

“This is due to the loose fit that plagues the standard KN95 design,” said Larry Weldon, who oversees Shawmut’s NIOSH certification program. “The differences in design between a KN95 and an N95 respirator are what account for the leakage. The ear loop design of the KN95 does not provide enough force to keep the edges of the mask tight against the face. The lack of a nose foam insert on the KN95 design does not prevent air leakage around the sides of the nose and upper cheeks. And lastly the flat-fold design with a stiff sealed seam down the middle of the face tends not to allow the very top and very bottom of the mask to conform tightly to the bridge of the nose and the bottom of the chin, opening gaps for air leakage.”

A New and Advanced Standard

Shawmut also announced that it is adopting the ASTM F3407 Respirator Fit Capability Standard across all its current and future N95 product lines and will be publishing the study data and future product measurements on its website on an ongoing basis. Shawmut’s NIOSH-approved Protex SR9520 N95 Particulate Respirator is the first N95 respirator on the market to publish its fit capability results using the ASTM F3407 Respirator Fit Capability (RFC) Standard. The results of the Shawmut evaluation indicate a higher probability the Protex provides an effective seal on almost every face size.

The ASTM F3407 Standard provides detailed instructions for performing a respirator fit capability test on a panel of human subjects that is representative of the U.S. workforce in terms of face shapes. The standard calls for measuring the number of airborne particles that infiltrate and accumulate inside a respirator while wearers perform a set of common workday activities, such as bending, turning their head from side to side, heavy breathing and speaking. The results are expressed as a ratio of the particles outside to the particles inside the mask, from 1 to 1 up to 200 to 1. This is known as a fit factor score.

OSHA specifies that, before workers can wear a half-facepiece air purifying respirator (such as an N95 FFR) for protection from a hazardous airborne contaminant in the workplace, they must achieve a minimum fit factor (similar to the ASTM RFC result) of 100, which means a leakage of about 1%. None of the three KN95s tested achieved the required passing RFC result of 100 on any of the 25 panelists, according to the results. The averages for the three models across all panelists were 3, 7 and 9. In contrast, the Shawmut N95 FFR achieved an RFC result of greater than 100 on every test subject, with an average score of 186 and 76% achieving the maximum score the test instrument measures of 200+, which indicates a leakage of about 0.5%.

“The fact that the KN95s couldn’t match the performance of the SR9520 was not a surprise to us; the SR9520 is probably the best fitting mask on the market,” Weldon said. “What shocked us was how low the KN95 scores were. A score of 3 means that approximately 33% of the particles are getting around the face seal. That’s roughly 70 times the rate of exposure of our SR9520 and far worse than any N95 we have tested.”

NIOSH understands how critical fit is to the performance of a respirator, but until recently, there had been no standard approach to evaluating the fit performance of respirators outside of individual certification testing in the field. To address this, NIOSH worked with ASTM to develop and publish the F3407 standard at the start of 2020. According to the NIOSH Science Blog, “The ASTM RFC Standard will enable respirator manufacturers to develop better designed models that fit the worker population. Respirators passing the RFC Standard test method are expected to have better fitting characteristics.” The method is so new, Shawmut could not find a certified third-party lab that could perform the test in the time frame required. The company ultimately recruited a panel and conducted the study in its own ISO-certified lab and subjected the results to detailed peer review by an academic respirator researcher. Shawmut believes it is the first study of its kind to be published.

“People focus on filtration numbers because they are easy to measure,” Wyner said.  “What they don’t get is what NIOSH calls in its science blog ‘the fundamental importance of fit’ to the protection equation. The press is talking a lot these days about ‘loose vs tight’ fitting, but when you start to do quantitative fit testing, you realize this can’t be assessed visually. If you don’t form a secure seal, the air will bypass the filter, getting sucked in through the smallest gap between the mask and the face.”

“Achieving high filtration is relatively easy; achieving a good seal in a mask that has high filtration and is comfortable enough to wear all day is a challenge,” Wyner added. “That’s why evaluating how well a mask fits a wide range of people, in accordance with the ASTM F3407 standard, is so valuable.”

Risks of KN95s

While Shawmut notes the number of KN95s tested in the study is relatively small and continues to collect data on KN95s and other respirators, the company remains confident the results accurately depict the risks to wearers of using even a verified KN95 mask. The three KN95 models tested were selected randomly, based on immediate availability, laboratory validation of the filtration efficiency and overall compliance with the KN95 GB2626 standard. Two were purchased from Amazon, the third from a health care distributor. All three KN95 models employed the standard flat-fold cup with ear loops design that is common to the category.

“You might find a KN95 mask that performs well on your face,” Weldon said. “But the probability of adequate protection for any particular wearer is low.”

Recognizing long-term value in the ASTM 3407 standard beyond the current pandemic, Shawmut plans to conduct and publish comparison testing on various respirator designs (e.g., cups, flat folds, duck bills, etc.) to understand performance tradeoffs. Shawmut also plans to assemble panels that reflect various underserved populations to surface differences in the fit performance of common respirator designs, and to evaluate potential alternative designs.

“It’s a powerful tool for our design and innovation processes, and we plan to make ASTM 3407 certification the standard for all our products,” Weldon said.


About Shawmut Corporation  

Shawmut Corp. uses materials innovation to improve people’s lives, employing expertise in fabric formation, coating, and laminating to deliver high-performance materials and components to the Automotive, Health & Safety, Defense, Protective, and Custom Laminating Solutions verticals. Shawmut applies its keen understanding of the unique challenges of materials for medical applications to its Protex™ line of personal protective equipment (PPE), including high-quality N95 respirators and non-surgical isolation gowns, manufactured in the U.S. To purchase Shawmut’s N95 respirator, click here. As a fourth-generation, family-run global company headquartered in West Bridgewater, MA, Shawmut employs over 700 employees worldwide in 10 manufacturing plants and seven commercial offices across North America, Europe, and Asia.  Shawmut can be found online on LinkedIn, Facebook, and Instagram. To learn more, visit

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