There is not much difference between KN95 and N95 respirator masks. Eventually, they both are rated to capture 95% of 0.3-micron particles. In short, N95 are the US standards. KN95 are Chinese standards. According to mask manufacturer 3M, " China's KN95s equivalent to US N95s". Both are tested at a flow rate of 85 L/minute and for filtration efficiency at capturing salt particles (NaCl).
Besides having so many similar properties, there are some differences between them. However, the differences are not the major ones and would be uninteresting and irrelevant to an average mask user. Here are the key differences:
N95 masks are approved and certified from NIOSH the US. KN95 face masks has not got such recognition yet.
N95 masks include a durable, firm and yet flexible nonwoven polypropylene fibre. They are mostly round, with the protrusion near the top to help cover your nose. Elastic string stretch around your head to hold a mask in place. There should be a label of "N95" on it.
KN95 mask looks almost alike N95 but, they feature a seam down the middle that makes it possible to fold it in half. It has ear loops to secure your face covering.
The KN95 mask manufacturer requires to run a mask fit test on humans with less than 8% leakage. N95 mask does not need to undergo such an obligation. However, this does not mean that fit tests are not helpful.
N95 masks have stricter requirements for pressure drop while inhaling and exhaling. It has to be less than 343 Pa for inhalation and 245 Pa for exhalation. The same is less than 350 Pa and 250 Pa for KN95 masks. That makes the breathability standards of N95 a bit stronger.
The FDA says N95 masks are not fit for children and people having a beard as it would not be able to secure a tight seal around their faces.
N95 masks are not reusable one must discard them immediately after use by placing them in a plastic bag. Some studies showed that KN95 are reusable effectively. Used KN95 masks showed effective filtration after spraying it with ethanol, air drying and vacuum drying it.