The study shows that cloth masks compete with some medical masks, but only N95s provide nearly complete protection

The study shows that cloth masks compete with some medical masks, but only N95s provide nearly complete protection

New research shows that while many cloth and medical masks fail against tiny airborne particles, simple hacks like over-masking or using staples can dramatically improve your protection, only N95 and Can99s respirators consistently keep you safest.

A current onePLOS oneThe study examined the effectiveness of medical and non-medical masks and respirators in issuing small aerosols.

Importance of Face Masks

Aerosol transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of the coronavirus disease 2019 (CoVID-19) pandemic, is well documented. Every individual has been advised to wear face masks during the pandemic to stop the spread of the virus. During the pandemic, the global shortage of personal protective equipment (PPE) led the general public to use cloth masks as an alternative.

In July 2024, the World Health Organization (WHO) recommended that everyone regularly wear masks in public settings. A wide range of masks and respirators are currently commercially available, including domestic and commercially manufactured cloth masks, certified medical and non-certified disposable masks, as well as KN95/KF94S and N95/CN99s.

It is important to systematically evaluate the aerosol filtration capacity of different masks and respirators, particularly from the wearer's perspective. This knowledge would be invaluable for public health advice on preventing airborne disease.

About the study

The current study recruited participants between March 2021 and April 2022. All participants were over 16 years of age and none had a history of respiratory illness or were allergic to latex. All participants' facial measurements were collected according to the US National Institute for Occupational Safety and Health (NIOSH) Bivariate Panel.

Importantly, the study focused on a specific, consensus-driven cloth mask—the Essex Mask—that was developed and optimized by a panel of community experts. The results for cloth masks therefore reflect this carefully designed model and cannot be generalized to all cloth masks.

Level 1 masks (Polar Bear and O2), Level 3 masks (Halyard and Primed), double-layer pleated cotton sheet masks without nose wire (Essex mask), non-certified masks (e.g.

A TSI 8026 particle generator was used to measure aerosols. The CSA-Z94.4-2002 protocol was used to demonstrate the filtering capacity of particles in the 0.02–1 μm range. Participants rated each mask based on subjective leakage, glasses fogging, and discomfort using Likert scales. The filtration efficiency of the oversize, that is, the use of an Essex mask for earloops as well as a certified level 1 and 3 mask as a base mask, was evaluated.

It is also important to note that the study evaluated filtration efficiency from a carrier protection perspective, not source control.

Study results

A total of 12 participants between 21 and 55 years old were recruited. This cohort included 58% of women and 25% were non-European. The filtration efficiency of a two-layer cotton fold Essex mask was 47 ± 5% when worn on earloops and 55 ± 6% on overhead ties. These values ​​were comparable to the filtration efficiency of Level -1 masks at 52 ± 6% (Earloops) and 56 ± 9% (Overhead). Level 3 masks showed variable filtration with one mask at 60 ± 6% and another at 75 ± 10%. KF94, KN95S and the KN95 lookalike mask fell between 57% and 77%. The certified respirators showed the highest filter efficiency of all masks at 97 to 98%.

The median filtration efficiency of the level 1 and 3 masks showed no further improvement after minor changes, including wearing a scrub cap, earbuds, or knotty music. However, both masks improved after braces were implemented to increase edge seals. In contrast to the neoprene clip, the silicone and fix-the-mask clips demonstrated a filtration efficiency of 79-87% in Level 1 masks. Notably, all braces tested in Level 3 masks yielded a median filtration efficiency (FFE) of 92–94%.

Excess weight had no influence on the leak values, but rather the mask type. Complaint levels varied from 2 (comfortable) to 6 (uncomfortable) across mask/respirator types. Medical masks and respirators were more comfortable than KF94 and KN95. Comfort scores were not associated with adjusted filtration efficiency.

Adjusted filtration efficiency was significantly associated with subjective ratings of eyewear fog and mask leaks, with the latter being the stronger predictor, explaining 22% of adjusted filtration efficiency. In contrast, glass fog explained only 4% of the variation. For masks with no proven leaks, the mean ± SD filtration efficiency was 86 ± 12%. The average values ​​with increasing leakage; However, these observations depend on the mask type. For KF94S and KN95S, participants found it difficult to detect leaks, and perceived leak levels explained only a small portion of the performance differences for these types.

Mask performance was much more strongly predicted by perceived leakage values ​​for Level 1 and 3 masks with and without hacks. For level 1 masks, FFE values ​​varied by 51% in individual trials. Up to half of the total variation in FFE values ​​for Level 3 masks was explained by leakage values. All respirator gowns were assigned the best perceived leak value of 1. This mask type also showed the lowest variation in performance between mask types. No association was measured between Menton-Sellion length and facial distances, bizygomatic distance, with a cord crossing the tip or bridge of the nose.

Notably, N95 and Can99 respirators performed at or near occupational safety health and safety standards for fit tested personal protective equipment, even without formal fit testing. With proper fit testing, their performance could be even higher.

This study is among the largest to systematically compare mask modifications (“hacks”) and overmasking strategies in real-world settings, providing greater statistical power and generalizability than most previous studies.

Conclusions

It was noted that well-designed cloth masks offered customized filtration for submicron aerosols in a similar range to Level 1 masks: approximately 50%. KN95S/KF94S and Level 3 masks filter around 70%. Overfitting with a cloth mask on ties or external clips resulted in around 90% filtration compared to Level 1 masks. Only N95s and Can99s passed near occupational health and safety standards. The results are specific to the protection of the wearer and may not apply to the source representation or all possible mask designs.

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