In protecting the wearer, two masks can be better than one, scientists say

In a pandemic during which our knowledge of the novel coronavirus is still evolving, two scientists have sought to clear some of the confusion over the performance of masks. They have recommended two masks rather than one in certain settings, and explained that a mask protects not only people around the wearer but also the wearer.

The recommendations by scientists Linsey Marr (Virginia Institute of Technology) and Monica Gandhi (University of California, San Francisco) appear as a commentary published by Cell Press, and have been reported by The New York Times. Several prominent Americans have already been seen wearing two masks; the NYT report cites the examples of American football coach Bill Belichick, President-elect Joe Biden and Senator Mitt Romney.

For maximal protection, Marr and Gandhi have recommended that members of the public wear either:

# A cloth mask tightly on top of a surgical mask where the surgical mask acts as a filter and the cloth mask provides an additional layer of filtration while improving the fit; or

# A three-layer mask with outer layers consisting of a flexible, tightly woven fabric that can conform well to the face and a middle layer consisting of a nonwoven high-efficiency filter material.

If these fit well, they write, these combinations canshould provide a 90% efficiency in blocking particles larger than 1 micron.

Recommended for maximal protection in Marr and Gandhi’s paper (Source: Cell Press)

“We are recommending two masks in settings where the patient is vulnerable (elderly or have a medical conditions) or indoors where conditions are crowded,” Gandhi told The Indian Express, by email. “The advantage of two masks (a cloth mask with a surgical mask combined) is that it blocks particles coming into the wearer at almost the same level as a medical grade N95 mask — 90-95%. This increases the safety for the wearer.”

The NYT article quotes Marr as saying that the point is not to make a mask airtight. Rather, the fibres in the mask fabric create a haphazard obstacle course for air and airborne particles.

The idea that multiple mask layers block the virus more effectively has been tested and shown by previous research. In a study last year in the American Chemical Society’s journal ACS Nano, researchers had identified a combination of two fabrics as possibly the best for filtering out respiratory particles — either cotton plus natural silk, or cotton plus chiffon (The Indian Express, April 20, 2020). That study and others have also stressed the importance of a proper fit.

Marr and Gandhi’s commentary, titled ‘Uniting Infectious Disease and Physical Science Principles on the Importance of Face Masks for COVID-19’, adds to various findings by underlining the role masks play in protecting the wearer.

“It was very confusing at the beginning of the pandemic when infectious diseases [scientists] were saying one thing (masks protect others) and physical scientists were saying another (masks protect you),” Gandhi told The Indian Express. “This article unites an infectious diseases doctor [Gandhi] and physical scientist researcher [Marr] to explain why masks protect you and others and are an incredibly important tool in the fight against Covid-19. Scientists from different disciplines need to come together more to present a unified message to the public on Covid-19.”