The particle filtration capacity (which prevents the virus from being breathed in or out) and the breathability (which measures to what extent they facilitate or hinder the passage of air) were measured and combined to establish a quality factor (QF) for each mask evaluated (see infographic<\/em>). \u201cOur study was a world first in combining filtration and breathability, which is important because lots of people don’t like wearing masks that make it difficult to breathe,\u201d says Artaxo.<\/p>\n The results confirmed what we already knew\u2014the importance of face masks to the epidemiological control of airborne diseases\u2014and provided details on the efficiency of different types. Considering filtration alone, the masks that performed best were the PFF2\/N95 types\u2014as expected\u2014which blocked 98% of the particles in the sizes tested (from 60 to 300 nm).<\/p>\n Surgical masks had a filtration capacity of 89% and nonwoven fabric masks with three layers filtered 78% of particles. Cotton masks proved less effective (between 20% and 60%) because there is more space between the threads. If the mask has a seam, the risk of penetration by the virus is greater still.<\/p>\n In terms of breathability, the standout was nonwoven fabric, followed closely by surgical masks. The PFF2\/N95 and cotton masks had a lower breathability index, although that does not mean they are difficult to use, even for long periods. \u201cWhen breathability is extremely low, it is difficult for air to get through the mask. This is bad because people want to take their mask off as soon as they can,\u201d says Artaxo.<\/p>\n After combining the filtration data and the breathability data, the quality factor of each type of mask was compared to the standard recommended by the World Health Organization (WHO). \u201cThe QF needs to be greater than 3 for a mask to meet the minimum filtration and breathability requirements proposed by the WHO,\u201d explains Morais.<\/p>\n In the USP\/IPEN study, the PFF2\/N95, surgical, and nonwoven masks all achieved WHO approval, with QFs of 13.2, 15.9, and 24.9 respectively. Homemade cotton masks, considering an average breathability of 40%, did not reach the recommended level, scoring just 1.4. \u201cEven though some types of masks have a very low quality factor, it’s important to remember that any mask is better than none at all. Although some are better than others, even the worse ones make a difference,\u201d says biomedical engineer Vitor Mori, a member of Brazil\u2019s Covid-19 BR Observatory.<\/p>\n<\/div>![](\"\/wp-content\/uploads\/2022\/04\/022-025_covid-mascaras_312-1-desktop-1.png\")
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The good news is that if these same two people were wearing properly fitted PFF2\/N95 masks, the chance of contagion in four times the contact time (20 minutes) would be just 0.1%\u2014a one in a thousand chance. Another conclusion of the study, led by Eberhard Bodenschatz, is that PFF2\/N95 masks (filtering facepiece respirators) provide 75 times greater protection than surgical masks, which for their part reduce the risk of contagion to a maximum of 10% if properly fitted.<\/p>\n
One of the most comprehensive investigations into the efficiency of face masks was carried out by Brazilian researchers. The group, from the Institute of Physics (IF) at the University of S\u00e3o Paulo (USP) and the Institute for Energy and Nuclear Research (IPEN), evaluated 227 different masks, from those made with cutting-edge technology, such as PFF2\/N95 masks, to surgical masks, synthetic or cotton fabric masks commonly sold in stores, and homemade face coverings. The results were published in the journal Aerosol Science and Technology<\/em> in April 2021. \u201cAt the beginning of the pandemic, USP\u2019s School of Medicine [FM] contacted Vanderley John, a professor from the Civil Construction Engineering Department at the Polytechnic School [POLI-USP], saying that they only had enough masks for another three weeks, both at the Hospital das Cl\u00ednicas and the University Hospital. Since the market was unable to meet the sudden high demand, FM suggested testing alternative fabrics for making masks,\u201d recalls IF doctoral student Fernando Morais, the study’s lead author.<\/p>\n The initiative became the Respire! (\u201cBreathe\u201d in English) project, led by John, who asked his IF colleagues to help test mask filtration capacities. To do so, the group adapted equipment usually used to monitor air quality in the Amazon and S\u00e3o Paulo to measure the volume of particles in the atmosphere.<\/p>\n \u201cOur team studies atmospheric aerosols and their impacts on the environment and climate. We already had the instrumentation\u2014which was actually funded by FAPESP\u2014needed to measure nanoparticles in the order of 10 nanometers [nm], which is 100 times smaller than the width of a hair. We also had aerosol generators capable of creating particles of the size we needed, of between 60 and 300 nm,\u201d explains IF physicist Paulo Artaxo, one of the coauthors of the study and Morais\u2019s PhD cosupervisor.<\/p>\n<\/div>![](\"\/wp-content\/uploads\/2022\/04\/022-025_covid-mascaras_312-0-desktop-true-1.png\")
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