In a recent study by Duke University in the United States, published this month in the Science Advances journal, it was found that the effectiveness of different types of masks vary widely, with some masks actually being counter-productive, in curbing the spread of COVID-19.
The above chart shows the filtration efficiency of various mask types for expelled droplets during speech. In the fight against COVID-19, this is, arguably, a more critical measurement than inward filtration efficiency. It prevents people with COVID-19, including asymptomatic cases, from unknowingly spreading the disease to others simply by talking to them. Filtering expelled droplets also prevents them from settling down on surfaces, such as table tops.
Filtered N95 masks still reign as king of the hill, offering filtration rates of 99.93%, followed by surgical masks with 99%. Most other re-usable masks made of fabric and polyester offer outward filtration levels between 67% to 95%.
However, certain types of masks should be avoided. N95 masks with valves and vents, for example, protect only the wearer, but not those around him or her. They filter only the air flowing in to the mask, but not air flowing out. So while they are more breathable, they do not prevent the user from spreading disease because droplets are expelled from the mask together with the air.
Neck gaiters, such as the one worn by a man in a dispute with a bus captain recently, actually increases the risk by about 9%. That's because it breaks larger droplets into smaller ones, which linger in the air longer, increasing the risk of transmitting COVID-19 to others.
We urge all Singaporeans to be socially responsible and don't just use scarves, neck gaiters or bandanas to get past the rules. Even valved or vented N95 masks are "anti-social", because they only protect you but not others around you.