Our inner layer fabric filter design provides maximum protection for particle size of 300 nano meters and above. WHO (World Health Organization) indicates that the primary air borne transmission of COVID-19 virus is through respiratory droplets of the size > 5000 nano meters.  

WHO guidelines

https://apps.who.int/iris/rest/bitstreams/1279750/retrieve

https://www.who.int/news-room/commentaries/detail/modes-of-transmission-of-virus-causing-covid-19-implications-for-ipc-precaution-recommendations