“The evidence is not sufficiently strong to support widespread use of facemasks as a protective measure against COVID-19. However, there is enough evidence to support the use of facemasks for short periods of time by particularly vulnerable individuals when in transient higher risk situations."
Results of a quick google scholar search produced a number of articles in the actual medical scientific literature regarding the effectiveness of cloth masks in slowing the spread of respiratory infections like Covid-19.
Here is one in the British Medical Journal, April 7, 2020. "Covid-19: What is the evidence for cloth masks?"
https://www.bmj.com/content/369/bmj.m1422.short
In discussing a systematic review of this question, which is a preprint available at
https://www.medrxiv.org/content/10.1101/2020.04.01.20049528v1 the authors of that review state in full (excerpt above)
"Based on the RCTs we would conclude that wearing facemasks can be very slightly protective against primary infection from casual community contact, and modestly protective against household infections when both infected and uninfected members wear facemasks. However, the RCTs often suffered from poor compliance and controls using facemasks. Across observational studies the evidence in favour of wearing facemasks was stronger. We expect RCTs to under-estimate the protective effect and observational studies to exaggerate it. The evidence is not sufficiently strong to support widespread use of facemasks as a protective measure against COVID-19.
However, there is enough evidence to support the use of facemasks for short periods of time by particularly vulnerable individuals when in transient higher risk situations. Further high quality trials are needed to assess when wearing a facemask in the community is most likely to be protective."
My view is pretty much in exact agreement with the authors of that preprint. Also please note that the authors did not in any way consider the possible negative consequences of making a broad scale community recommendation to wear cloth masks.