You may have seen people wearing KN95 masks – this is the kind I use, and I can tell you a little bit about them. They can be fitted well, and are easy to breathe through. A couple times I have ridden out of my building and forgotten to remove it for the ride home.
But since they have five layers, it’s a little weird that they are so easy to breathe through. What gives?
“At microscopic scale, everything is sticky” This video explains how the Van Der Waals effect underlies the physics of the N95 mask:
Including this extra picture just because I like details