A pack of 2 replacement filters for the Respro Metro mask.

The Metro filters are specifically intended to deal with the gasses, vapours and paticulates encountered in an urban environment. Ideal for daily commuters who ride in slow moving traffic.
These are the same filters as the one included when you buy the Metro face mask, but are actually compatible with any of the other Respro masks, meaning you can change your filter type when your ride changes, without changing the mask itself.

The lifespan and effectiveness of each filter depends on where you ride and how often, but as a rough guide Respro recommend replacing a filter after 69 hours of use. For a half hour commute each way, five days a week that makes about 7 weeks, so changing every 1 1/2 to 2 months should do it.
If you spend significantly more time in traffic than that you should consider changing more regularly.