The 3 studies I've seen all showed 40-50% of infections were from people without symptoms:
https://nature.com/articles/s41591-020-0869-5
https://wellcomeopenresearch.org/articles/5-58
https://medrxiv.org/content/10.1101/2020.03.05.20031815v1
There's also a mechanism paper:
https://www.nature.com/articles/s41586-020-2196-x_reference.pdf
https://nature.com/articles/s41591-020-0869-5
https://wellcomeopenresearch.org/articles/5-58
https://medrxiv.org/content/10.1101/2020.03.05.20031815v1
There's also a mechanism paper:
https://www.nature.com/articles/s41586-020-2196-x_reference.pdf
These are all listed in the relevant section of the FAQ https://www.fast.ai/2020/04/20/skeptics-masks/#shouldnt-only-sick-people-wear-masks