The usable lifespan of the ‘Combination’ filter is based on the characteristics of the active urban cyclist. If the mask is being used for any other activity it still applies, but the different breathing rate and activity would put the lifespan of the filter at a proportionally shorter or longer time. For example; If the breathing rate is half that of a cyclist then the effectiveness of the filter would be twice as long. For cycle commuting on a daily basis we recommend that the filter should be replaced every month or every 69 hours, whichever is sooner.  A Combination Filter provides the broadest spectrum of filtration for gases, vapours and particulates common in urban environments with poor air quality.