One of the most politicised scientific issues of 2020 was the question about whether face-masks stop the spread of COVID-19. I trust we can agree that this is notable without requiring specific examples.
In particular:
When worn by members of the public who are healthy, are cloth facemasks effective at slowing the spread of COVID-19?
Cloth facemasks refer to the non-disposable, often hand-crafted, masks that have been widely adopted, often in response to government mandates. Their quality may vary; if your evidence is focused on particular specifications (number of layers, material, age, etc.) please make that clear.
Note that this question is about effectiveness (not efficacy), so answerers and voters are invited to weight evidence about the spread of COVID-19 in real-life conditions above evidence from lab experiments, and in turn, evidence from lab-experiments above theoretical models.
This question is one of a number of similar questions on Skeptics.SE. For a master list, see here
