It looks like there’s some discussion in the previous comments on masks. I’m going to add my two cents here, but you might want to look at the comments for the last post.
I’m only going to talk about my experience with N95 and KN95 masks.
This is a medical grade 3M Medline N95 mask that I wore when caring for my parents in the Dakotas (it was a gift from a friend of theirs). Things to note are the foam on the nosepiece, the stiff construction of the mask to ensure that as much of the mask surface is involved in filtration as possible, the two plastic bands that go over the head and hold the mask very tightly against the face, and the substantial metal band at the nose. It is also quite uncomfortable to wear for long periods of time because of the force with which the mask is pushed onto your face. Also, I only had a couple, so this mask has almost certainly lost some of its filtration ability. I don’t wear it anymore.
This is a pretty typical KN95 mask with earloops, purchased from Amazon. KN95 is the Chinese standard for N95 masks. The FDA has approved certain of these masks for use under emergency orders during COVID-19. Appendix A at this link will give you a list of manufacturers certified by the FDA. This particular mask was purchased in a lot of 20 from Amazon, and it claims to be on the FDA list, but there was no way to make sure it was. It uses earloops, which are more convenient than a headband but not as effective. The nosepiece metal is weaker than the N95 above, it has no seal around the nose other than the metal, and it is tough on my ears. But, I wear it as my go to mask because it seals pretty well and I have a fair number of them. It has less of an effective seal as the N95 above, but it is more comfortable.
This KN95 has headloops and is pretty definitely on the FDA list. I purchased it from a company called BonaFideMasks. It took them 3 weeks to deliver it in December. It came with a seal with scrape-off coating that had a code underneath. There was a QR code on the seal — by scanning it with my phone I was directed to the manufacturer website and told that the mask was one of theirs. Two important points: First, the mask fits almost as well as the N95. Second, my wife, who has a small face and for whom the other KN95 doesn’t fit well at all, finds that this mask seals pretty well. This is the one I’d recommend if you’re in the market for an “almost as good as an N95” mask, because the headloops are much more effective than earloops.
This is a PAPR. A nurse who trained with this and N95s say this is far superior and you can actually work a full shift without discomfort. I haven’t seen any of these in the grocery store, yet.