What the NOISH Certification Means:

The N95 mask is certified by the National Institute for Occupational Safety and Health (NIOSH) to ensure the mask has been tested and manufactured to a standard that makes it capable of filtering very fine particles that do not  contain oil, even the most difficult to filter at 0.3 micron in size. The period at the end of the last sentence is approximately 615 micron wide so you can appreciate that these particles cannot be seen with the naked eye.