WHO has released an updated mask guidance in June 2020 which can be found here:
www.who.int/emergencies/diseases/novel-coronavirus-2019/advice-for-public/when-and-how-to-use-masks
It has updated information on a new study released on fabric masks which explains how many layers are ideal for the best filtration and breathability combination and what their composition should be. We also describe how to best care for your mask including storing it and laundering it.