A pack of ten PM 2.5 filters consisting of 5 layers of micro filtration including an active carbon layer to help neutralise toxic air-borne chemicals. The PM 2.5 filters have a pore size rating of 2.0 microns and provide effective filtration. Filters may be used for up to one week with infrequent use.Please note that this product cannot be returned due to Health & Hygiene reasons if the packet has been opened.