An N95 dust mask can protect the lungs from dust particles as small as 0.3 micrometers (300 nanometers) and smaller. Specifically, N95 masks have a filtration efficiency of at least 95% for particles around 0.1 to 0.3 microns in size, with even higher efficiency (up to 99.5%) for particles around 750 nanometers (0.75 microns)
. The filtration mechanisms in these masks work effectively on particles ranging roughly from 0.1 microns to 1 micron, including dust, fine aerosols, bacteria, viruses, and other airborne particulates
. Particles smaller than 0.3 microns, such as some fine aerosols and viruses, are filtered through diffusion and interception processes, while larger particles are filtered by impaction and settling. In summary, a properly fitted N95 mask protects against dust particles down to about 0.1 microns in size, with optimal performance around the 0.3-micron particle size, which is considered the most penetrating particle size for filters
