April 29, 2020

A study on face masks has identified a combination of two fabrics as possibly the best: either cotton plus natural silk, or cotton plus chiffon. If the fit is good, such homemade masks can effectively keep out aerosol particles.


  • An aerosol is a suspension of particles or droplets in the air. The virus that causes COVID-19 is thought to spread mainly through respiratory droplets, particularly when an infected person coughs or sneezes.

  • The World Health Organization (WHO) defines two size ranges for droplets through which respiratory infections can be transmitted — 5-10 microns in diameter (respiratory droplets) and less than 5 microns in diameter (droplet nuclei). One micron is a millionth part of a metre.

  • It is respiratory droplets (the larger size range) that are thought to be the primary route of COVID-19 infection. Airborne transmission, which is through droplet nuclei (the smaller size range), was not reported in a large study in China, the WHO notes.