COVID-19: Which masks are effective?

Scientists develop low-cost method to test effectiveness of different kinds of masks against viral droplets

Using widely available tools, scientists have developed a simple method to visualise how effectively different types of masks prevent the spread of droplets that could contain novel coronavirus particles, an advance which could aid small scale mask producers to optimise designs, and help community outreach organisations demonstrate proper mask fitting procedures.

The technique, described in the journal Science Advances, is still in the early stages, and has so far only been tested in a small group of people, the scientists said. According to the researchers from Duke University in the US, the preliminary, proof-of-principle findings suggest that professional-grade N95 masks, surgical or polypropylene masks, and handmade cotton masks may all block much of the droplet-spray produced when wearers speak.

However, they said bandanas and neck fleeces likely provide little protection, as the scientists observed that more droplets are expelled through these materials. They said this is likely because the materials break up larger droplets as they pass through the material.

In the study, the scientists evaluated the effectiveness of 14 different types of masks and other frequently substituted face coverings, using a simple approach in which either one male speaker or, in some cases, four speakers wore each mask while standing in a dark enclosure. The speaker then uttered the phrase "stay healthy, people" five times in the direction of a laser beam, which scattered light from the droplets released during speech, the study noted.