Originally Posted by andrey_gta
That second black filter is the permanent Charcoal Filter. Many people choose to cut it out since it is molded into the air box and is only there to prevent some emissions particles. The e39 m5 first had it and people would always remove it on m5 msg boards
Look up info on it on e90post.
The thing is that it is not a black filter. It is a white paper filter. In the instalation instructions it says to remove the back of the box and original filter and then reuses the back of the box but does not specify whether the paper filter should also be reused or not but implies that it is not reused.