The Flinders University study tested a range of masks on their ability to block two types of aerosols - one the size of those produced by coughing and another small enough to be inhaled into the lower respiratory system.

The best-performing fabric masks filtered 97-99 per cent of the virus particles of both sizes.

A mask made with two layers of reusable shopping bag fabric and one layer of cotton, as per Victorian Department of Health and Human Services guidelines, filtered 98.6 per cent of the cough-sized virus aerosols and 99.1 per cent of the smaller aerosols.

A mask composed only of two layers of cotton filtered 55 per cent of the cough-sized aerosols and 93 per cent of the smaller aerosol.

The researchers say while a 50 per cent reduction might not seem particularly effective, it could prevent thousands of deaths in areas of high transmission.

Studies have shown that if 80 per cent of the population were to wear even a poor performing mask in areas of high transmission such as New York City, the number of COVID-19 deaths could fall between 17 per cent and 45 per cent.

Australian Associated Press