Okay let me explain more about it
ASTM (American Society of Testing and Materials) ASTM is one of the trusted quality test which grade the facemask. In order to have the grade, ASTM need to full fill the followings
BFE - Measures how well the medical face mask filters out bacteria.
PFE - Measures how well a hospital mask filters sub-micron particles with the expectation that viruses will be filtered in a similar manner.
Fluid resistance - Reflects the surgical mask’s ability to minimize the amount of fluid that could transfer from the outer layers through to the inner layer.
ISO Certification - All medical face masks must be tested to an international standard (ISO10993-5, 10) for skin sensitivity and cytotoxic tests to ensure that no materials are harmful to the wearer.
Facemask which have tested with ASTM will have categorized as Type I, TYPE II and Type III
Type II and Type III will provide you the best protections as BFE > 98%
Hope this is clear for you