NIOSH N95 is all I've used for 18 months, and the only thing I would ever use. The U.S. government (CDC) badly misled the public regarding this, and did so quite intentionally using the justification of protecting the supply for front-line / healthcare workers. They only fully admitted to this in the past two weeks when they began strongly recommending "KN95". I have no doubt that many have suffered due to that misleading initial recommendation. Fortunately I had some background knowledge up front and knew better. NIOSH N95s are highly effective (if properly fitted [fit tested] when used, of course). Be aware that although the more widely available KN95 should be as effective in terms of filtration, that standard allows higher pressure differential (more restrictive / more resistance to air flow), and thus are more difficult to use, and this is a particular issue for those with compromised breathing. If you have such issues, definitely stick to NIOSH N95.
Going on two years ago,
actual KN95's were better than the cloth/surgical masks and neck gaiters that were popular - the media
specification is substantially similar to N95 and the fitment at least pulled the media against the face. The trouble of course was finding a reputable supplier - the 'zon was full of knockoffs that clearly didn't make the filtration spec and even managed to cockup the semistandard 2-part welded construction.
As at least 6 months ago, N95s again became plentiful thus the argument for KN95 greatly weakened. The construction of most 3D N95s is superior to the 2D folding KN95 and the around-the-head straps provide for a superior seal against the face.
I'm still lousy with KN95s so I'm still using them as replacement filter media for some knockoff RZ masks I obtained early on. I then place a surgical mask over the exhaust valves primarily for the benefit of those around me. My exposure is hardly occupational so I'm OK with the middling performance relative to actual N95s and unlike every other option I've tried, the arrangement doesn't fog my glasses
like it was a primary design consideration.
N / P100 is also the 'gold standard' for particulates (including viruses), but are generally off limits for virus protection in the current environment due to the fact that they always (or nearly so) incorporate an exhale valve, which is forbidden in many environments. Don't even try to get on a plane wearing one.
For
casual usage I'll slip a surgical mask over my P100 setup's exhaust valve; I only expect to do this if I'm at a place like the local makerspace where I might need to wear a mask continuously for hours, it also works as PPE in the various shops, and can't take it off at all and thus want the ease of breathing without adjustment of the mask.
Most so-called 'cloth masks' (as recommended by our government) are largely ineffective. So-called 'surgical masks' are only marginally better, but very ineffective compared with N95.
The whole improvised PPE push ~Q1 2020 was about reducing overall numbers in terms of cases while the purpose of discouraging mass usage of N95
et al was about protecting the supply chain for healthcare. I remember that just about
to the day that the first guidance on face masks was given, N95s vanished from the shelves of local big box stores - both the likes of megalomart and the orange despot.
From a public health perspective any meaningful reduction is a worthwhile avenue, but from an individual perspective crap methods that do little to protect
you are a tough sell. I do wonder if the push for cloth masks - with the filter pocket that almost no one used and didn't really matter since fitment was more for comfort than perimeter seal - was a clever bit of social engineering knowing that customization was likely which would see more usage than the likes of more-effective KN95/FFP2/KF94/* masks and would thus bump macro numbers more.
