This is a very different thing to particulate masks and not to be confused with the above. For a start, particulate masks have a release valve, which AFAICT is body for protecting other people, which is the whole point.
Jeremy Howard, Cloth masks can protect the wearer:
As we all know now, the science shows that DIY masks are particularly good at protecting those around you, in case you're infected with COVID-19. But that doesn't mean that you can't do a lot to protect yourself too.
Unfortunately, many public health bodies still incorrectly claim that there is no evidence that DIY masks are useful at protecting the wearer. There's actually plenty of evidence they can. Effective protection for the wearer of a mask depends on three critical things:
Much more useful summary and advice there.