F1 is our standard filter consisting of two filter layers, the outer particulate filter and the internal active carbon element. The outer layer of the F1 filter is capable of trapping particulates down to .1 microns in size. The inner layer, known as the Active Carbon element is effective towards gases, fumes and odors. Combing the two technologies this filter has been laboratory tested to be 99.9% effective. Common uses: Low intensity activities, high gases/fumes/odors. This filter is universal with all styles of RZ Mask models, in particular, the M1 Neoprene and M2 Mesh.