Double-Masking Benefits Are Limited, Japan Supercomputer Finds

(Bloomberg) -- Wearing two masks offers limited benefits in preventing the spread of droplets that could carry the coronavirus compared to one well-fitted disposable mask, according to a Japanese study that modeled the dispersal of droplets on a supercomputer.

The U.S. Centers for Disease Control and Prevention recommended double masking in February, saying Americans should wear a cloth mask over a disposable mask, the latest change to its recommendations on face coverings.

But a similar benefit can be had with just one correctly-fitted mask, according to the research carried out in Japan by the Riken research institute and Kobe University using Fugaku, the world's fastest supercomputer co-developed with Fujitsu Ltd.

“While some improvement can be had wearing a cloth or urethane mask over a loosely-fitted nonwoven mask, there's not a large difference when compared with one properly-fitted nonwoven mask,” the study said.

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Wearing one tightly-fitted disposable mask prevented the spread of 85% of particles that could carry the virus, while wearing two masks lifted that only to 89%, the simulation found. One regularly fitted mask captured 81% of the droplets, while one loosely fitted mask captured just 69%.

However, the study noted that a tight fit and avoiding gaps in the mask was crucial to preventing the spread of droplets. The CDC guidance did note that the goal was to have the second mask push the edges of the inner mask against the face to provide a snug fit. Wearing two nonwoven masks was not recommended, the study said.

The supercomputer has previously been used to demonstrate what types of mask work best, and model the benefits of ventilation in preventing the spread of the virus.

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