[neckardt]

You mean a mask which filters both on inhale and exhale? N95 masks do a decent job of that, although I'd guess there's still some leakage on exhale (not designed for that). N95s are still sold out in my area, so I got some KN95 which I use. The CDC tested some of them for effectiveness, many of them got pretty high marks: https://www.cdc.gov/niosh/npptl/respirators/testing/NonNIOSH...

[davak]

Some of the KN95s have been found to be counterfeit. Some of the ones we tested were no better than a cloth mask. When buying KN95s, please check that they've been validated by the CDC's list.

If it's legitimate KN95, it probably protects at least as good as a medical mask but probably not as good as a N95. This is because KN95s are not designed to form a complete seal so many folks will have some leakage around the edges. This is the reason that you see many systems 3d printing molded frames to improve the KN95 fit and decrease leakage.