What is the best mask for protection against Covid-19?

Evaluation of Cloth Masks and Modified Procedure Masks as Personal Protective Equipment for the Public During the COVID-19 Pandemic – JAMA 2020 December 11

Key Points
Question What are the fitted filtration efficiencies (FFEs) of consumer-grade masks, improvised face coverings, and modified procedure masks commonly used during the coronavirus disease 2019 (COVID-19) pandemic?

Findings In this comparative study of face covering FFEs, we observed that consumer-grade masks and improvised face coverings varied widely, ranging from 26.5% to 79.0% FFE. Modifications intended to enhance the fit of medical procedure masks improved FFE measurements from 38.5% (unmodified mask) to as much as 80.2%.

Meaning Simple modifications can improve the fit and filtration efficiency of medical procedure masks; however, the practical effectiveness of consumer-grade masks available to the public is, in many cases, comparable with or better than their non-N95 respirator medical mask counterparts.