The study that finds 70% effectiveness was based on just 4 people, one of whom couldn't produce virus particles even without a mask. Another most serious study

The study that finds 70% effectiveness was based on just 4 people, one of whom couldn't produce virus particles even without a mask. Another most serious study based on over 1500 hospital workers found that cloth masks let through over 95% of particles. That more serious study was done in 2015 but there's no reason to think it would not still be correct.