That is incorrect. N95 and P100 masks are available with and without valves. One of the purposes of the exhaust valve in a respirator like this is so that moi

That is incorrect. N95 and P100 masks are available with and without valves. One of the purposes of the exhaust valve in a respirator like this is so that moisture from exhalations does not build up in the mask, forming droplets, which then drip onto the finish surface that you are staining/sealing/painting. This is a problem when performing fine finishing as a drop of water can wreak havoc in the finish you are applying.