Aeropress filters are simple little paper or steel disks which are inserted into the cap. The coffee grounds are then poured into the cylinder, on top of the filter, and pressed.
There are two variations of these filters.
Paper Filters
These come with your coffee maker and are by far the most common type of filter used. These filters are cheap and effective. You can get replacement filters by the hundreds very cheap.
Steel Filters
These are the newest, latest and greatest accessory for your Aeropress. These metal filters are an effective and reusable filter system for the Aeropress. You can get one filter and never have to worry about buying filters again. There are many happy users and these filters are just as effective as paper filters. Find out more info about steel filters here.