April 11, 2021

Fitting the mask correctly is as important as the material it is made from


When choosing a mask that protects against coronavirus, choosing which filter material it is made of is as important as whether it fits the user properly. What’s more, when a high-performance mask, such as an N95, KN95, or FFP2, doesn’t fit the user’s face properly, it doesn’t perform any better than a basic fabric one.

This is the main conclusion reached by a group of researchers from the University of Cambridge (United Kingdom), whose results have been published in the magazine PLoS ONE.

“We know that unless there is a good seal between the mask and the user’s face, many aerosols and droplets will seep through the top and sides, as many people who wear glasses will know,” says Eugenia O ‘Kelly, researcher at Cambridge Engineering Department and author of the article.

For this study, seven participants were fitted with different models of N95 and KN95 masks (certified by US and Chinese regulations respectively), surgical and fabric, verifying if they were well adjusted. They were then subjected to different tests that accounted for the concentration of particles on the inside and outside of the mask.

As the authors expected, the N95s were the ones that offered the best filtration results, although they found that most of the masks of this type did not fit correctly on the faces of the participants.

According to their results, N95 masks filter more than 95% of airborne particles when properly fitted. However, the level of filtration offered by poorly fitted was comparable to the level of surgical or cloth masks. “It is not enough to assume that a single N95 model will fit the majority of the population,” O’Kelly says.

Elements of the mask itself, such as the width of the edge that comes into contact with the skin, can be a “critical” characteristic for the fit of the mask. The masks that fit the participants’ faces the best, they explain, tend to have wider, more flexible flanges around the edge.

Similarly, small anatomical differences in subjects can also affect fit. “A nose one centimeter wider or cheeks slightly fatter can influence the fit of a mask,” says the researcher.

Therefore, those responsible for this study conclude that it is essential to have a wide variety of mask models and sizes, “since it cannot be assumed that one model protects the majority of users”

How to better fit the mask

As the researchers point out, it was sometimes very difficult for study participants to find deficiencies in mask-fit visually.

The type of mask we use matters, but we cannot ignore the placement and the time of use

Gemma del Caño
– Pharmacist, food safety specialist and disseminator

“I usually breathe in front of a mirror to detect possible gaps. There where the glass is fogged is where there may be a gap”, explains to SINC Gemma del Caño, pharmacist, specialist in food safety and popularizer. This specialist believes that there are aspects about the use of masks that we have not yet mastered. “The type we use matters, but we cannot ignore the placement and the time of use, which should be 8 hours in the case of FFP2 and 4 hours in the case of surgical or hygienic ones,” he says.

Regarding the adjustment of the masks, del Caño suggests several formulas to prevent air from entering and leaving through small gaps that can be formed when fixing it on the face.

“To properly fit a surgical mask there are different alternatives. A knot can be made at the beginning of the gums, narrowing that little gap that remains in the cheeks. You can also use utensils so that the gums do not hurt, but placing them above the ears so that they are not hollow, “he says.

In addition, he explains that new tools are reaching the market every time that facilitate and improve this work, such as adjusters.


For those adults who have smaller heads, the expert recalls that there are surgical masks of different sizes for children, and that these can be a solution. This possibility, however, does not occur in the FFP2 type, since they were originally designed to protect certain health or industrial workers.

The FFP2, for its part, “seems to fit better than the surgical ones,” says del Caño. This quality, along with the fact that they have bi-directional filtering, can make them more suitable for certain crowded and unventilated places, the expert points out.

“We have to know that each mask is better for each specific moment. That is, if we go out for a walk, a reusable toilet is more than enough; but if we are going to get into the subway, it is still more appropriate a FFP2 that fits well, both to protect ourselves and the rest of the people, “he says.

Finally, he clarifies that wearing two masks only makes sense when it serves to improve the fit of the one that is stuck to the face. In this case, it would only be advisable to place a cloth one above the hygienic one. “The goal is to fit better, not filter more. When you already achieve 98% filtration, adding a second mask will not improve filtration,” he concludes.

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