Covid-19: ‘Proper fit’ of face mask more crucial than material, says study

A team of researchers who carried out a study to examine the effectiveness of different types of face masks found that the fit of a mask is as important, or more important, than the material it is made of, to protect individuals from Covid-19.

The researchers, from the University of Cambridge, carried out a series of different fit tests. They found that when a high-performance mask — such as an N95, KN95, or FFP2 mask — is not properly fitted, it performs no better than a cloth mask.

Minor differences in facial features, including the amount of fat under the skin, make significant differences in how well a mask fits.

The results, published in the journal PLOS One, suggested that the fit-check routine used in many healthcare settings has high failure rates. This is due to minor leaks that may be difficult or impossible for the wearer to detect.

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The current study with a limited sample size, only evaluated the impact of fit on the wearer of the mask. The team now intends to examine how fit a mask should be to provide protection to others.

First author, Eugenia O’Kelly from Cambridge’s Department of Engineering, said: “We know that unless there is a good seal between the mask and the wearer’s face, many aerosols and droplets will leak through the top and sides of the mask, as many people who wear glasses will be well aware of.”

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“We wanted to quantitatively evaluate the level of fit offered by various types of masks, and most importantly, assess the accuracy of implementing fit checks by comparing fit check results to quantitative fit testing results,” Kelly added.

Methodology

For the study, seven participants first evaluated N95 and KN95 masks by performing a fit check, according to NHS guidelines.

Participants then underwent quantitative fit testing — which uses a particle counter to measure the concentration of particles inside and outside the mask. They wore N95 and KN95 masks, surgical masks, and fabric masks. The results assessed the protection to the mask wearer, which is important in clinical settings.

The researchers also found that N95 masks offered higher degrees of protection than the other categories of masks tested. However, most N95 masks failed to fit the participants adequately.

In their study, the researchers found that when fitted properly, N95 masks filtered more than 95 per cent of airborne particles, offering superior protection. However, in some cases, poorly fitted N95 masks were only comparable with surgical or cloth masks.