This 1st stage very thin filter is used in front of the 2nd stage filter in applications where you would encounter a lot of oily or gummy substances such as CaCao butter or heavy oil based paints.
It saves you from having to replace more expensive filters by using this one time disposable filter barrier.
We recommend you throw it away after every application but of course this depends on your judgement as to how dirty it is. However, if you notice that it is getting too dirty even as you are spraying, you should consider replacing it more often and as needed to maintain proper air flow.
Please keep in mind that a dirty filter will reduce the vacuum efficiency of the unit and cause a reduction in air flow which means that not all paint oversprays are caught by the system.
BE WISE and replace your filters often.