“This study is the first RCT of cloth masks, and the results caution against the use of cloth masks… Moisture retention, reuse of cloth masks and poor filtration may result in increased risk of infection. Penetration of cloth masks by particles was almost 97% and medical masks 44%.”
MacIntyre, C Raina et al. A cluster randomised trial of cloth masks compared with medical masks in healthcare workers. BMJ open vol. 5,4 e006577. 22 April 2015, https://bmjopen.bmj.com/content/5/4/e006577.