mki mask filters 10 pack. 5ply carbon filters to be used in conjunction with the mki face mask. these filters are not approved for use in a medical environment, nor are they classed as personal protective equipment. mki store ltd make no claims about the medical benefits of using this product. for official government guidelines visit gov.uk. the effective working life of the mask filters depends on a number of factors, such as: the breathing rate of the user, ambient levels of pollution, daily usage, hygiene levels. taking these factors into account; if used every day; we recommend that the filter be replaced every 2 weeks. once purchased, mki store ltd take no responsibility in the maintenance of this mask and filters. Please note that in the interest of hygiene and safety, this item is non-returnable.