These 4 layer Carbon Filters are made of non-woven activated charcoal microfiber, (Replacement filters for item 935421 / Black Air Vent Masks). They are known to provide protection against non-oil based aerosols and particles from grinding, sanding, flour, pollen, metal, and dust. Each Filter is 3.5x4.9 in size. Duration time for the filter depends on the breathing rate of the user and the pollution level. We recommend replacing the filter every 24 hours if the mask is used extensively in heavy dust exposure to things such as; grain bins, off-roading, construction/demolition, etc. Discard used filter when replaced. Activated Carton. Non-woven Fabric.