Alright, so individual viral particles, like that of COVID-19, are actually way way smaller than the weave of most fabrics. However, they do not just float around in the air on their own. They fly around in droplets of moisture in the air, like the moisture of our breath!
Here, we can see how we breathe out big volumes of air and moisture when we talk and breathe 1Thanks to Matthew E. Staymates for providing this footage. Using schlieren imaging, we can see how much air we regularly breathe out. (Click the links to find out more!), where COVID-19 can use to transport themselves around. These droplets of moisture are heavy enough to fall down after about 2 metres or so (which is why social distancing is important!). However, these droplets can evaporate into smaller droplets that are small enough to be carried away by air currents and potentially into someone’s mouth.
With a mask on though...
See how it blocks and constricts the air coming out? Those large droplets of moisture that might have COVID-19 particles in them get blocked by the mask. If you’re wearing a mask and it feels hot and humid in there, that means it’s working! And whatever viral particles that do get through, they lose so much momentum from traveling through and around the mask that they don’t even travel very far!