SARS-CoV-2 in the hospital environment and risk of COVID-19 nosocomial transmission
A document produced by SAGE states the following.
Evidence on efficacy of cloth face-coverings (non-medical masks):
There is limited evidence regarding the respiratory protection that non-medical / homemade masks can offer for the wearer, and there are no established quality standards for self-made face masks. One study reported a low filter efficiency (3-33%), and high penetration (up to 97%) of NaCl aerosol particles in homemade masks (42). A trial comparing the use of cloth and medical masks by healthcare workers also showed penetration of microorganisms by 97%, compared with a rate of 44% for medical masks (43).