Lot of two New in Box, size Small Cambridge brand, The Admiral mask Valved, Navy blue Selling two separate lots of these, see my other listings and bundle for shipping discount Per their website - Three Ply-Micro Particulate Layer The Three Ply-Micro Particulate Layer serves as the masks second line of defence and blocks particulates such as PM2.5 – emissions typically emitted from the combustion of wood, gasoline, diesel, and oil. This layer also filters 99.7% of particles as small as PM0.3, because the high surface area captures a greater percentage of particles as they pass through the filter.