The main difference between N90 and N95 masks is the different protection levels. Where N means not suitable for oily particles, while 90 and 95 represent the protection ability of the masks. Different protection levels represent the different protection and filtration ability of the masks, i.e. different ability to block micro-dust, bacteria and virus filtration. N95 mask indicates that under the testing conditions specified by the National Institute of Occupational Safety and Health (NIOSH) standard, the mask has a filtration efficiency of 95% for non-oily particles such as dust, acid mist, paint mist, microorganisms, etc., while the filtration efficiency of N90 mask is 90%. Therefore, N95 masks have better protection than N90 masks.