Breather filters GN 882 are used when the air exchange is to be allowed between the inside of the container and the ambient air. The filter function is marked by a blue colour ring.
The filter prevents air-borne particles (e.g. dust) from being carried from the outside to the inside of the container. It also ensures that e.g. oil particles do not escape to the outside.
The above diagram shows the air passage as a factor of the differential pressure.