Since COVID-19 turned our lives upside down six months ago, scientists have been scrambling to learn as much as they can about this deadly disease.

There is still a lot of research to be done. But back in April, a team at Duke University set out to answer a question that was on everyones minds (and still is): How effective are face masks at reducing the transmission of respiratory droplets that carry the coronavirus ?

The researchers, who released their results in early August, found that a fitted N-95 mask (without a valve) and a three-layer surgical mask are the most effective at preventing the spread of aerosol droplets that might carry COVID-19.

This study is one of the first to focus on the effect of a mask at stopping its wearer from spreading potential coronavirus aerosols (rather than protecting the wearer from those nearby).

All the testing in the past had to do with protecting the individual wearing the masks, not considering protecting other people, Eric Westman, one of the studys authors, told HuffPost. So, for example, the N-95 mask with a valve is the best [at protecting you], but the valve allows you to exhale unfiltered air, so its not the best mask when looking at whether it protects other people from you if youre sick.

The team avoided assigning a definitive ranking to the masks in the study which has significant limitations and faced criticism when the results were published but agreed that a fitted N-95 mask (one without a valve) is one of the most effective face coverings currently available.

Because research on the efficacy of certain types of masks is still scarce, these results are useful in that they provide us with more information on the importance of wearing masks.

How was the study conducted?

To analyze 14 different masks which Westman said were chosen because they were conveniently available the researchers came up with a relatively simple method that involved a black box, a lens, a laser and a cell phone camera.

The idea of testing real people with a laser is novel, Westman said. Before this pandemic nobody really considered doing that.

The team cut a hole in the front of the box and two thin slits across its left and right sides. A laser beam shined a light across the slits while a cell phone camera was positioned on the back of the box. Study participants were then asked to speak through the hole while the cell phone recorded the way the light moved in different directions by the speakers respiratory droplets. A computer algorithm did the rest.