Im prettu sure its up.

End of story

I am also confused Air Flow direction on E53 Cabin Filter
 

when I pull the cabin filter out, it seems to be the debris is on the bottom side which indicate the air flow is going up. But installation steps which comes with say the air flow arrow should point down.

So which way shall I install the cabin air filter?

I got conflict information here and youtube.

Really BMW should have a mark on the cabin air filter cover so no confusing on this topic.

Follow the way the air flows into the filter box, through the filter, then on into the plenum and into the HVAC's blower.

If debris is in the bottom of the box, and the lower side of the filter is where the dirt is and the plenum (tunnel where air flows into the HVAC system) is on top...then the air is flowing from the bottom up though the filter into the plenum...thus the arrows should point upwards.

Yes, there are lots of owners and videos on youtube that have the microfilter/pollen filter installed incorrectly. :cool:

Indeed, the flow arrow should point to upward. I took out cabin air filter just a moment ago, I did see the intake air entrance is below the filer. It is obvious air can only flow from bottom to the top.

So this matter is resolved. FLOW ARROW SHOULD POINT TO UPWARD!!!

Cool now that the directions been settled the temp outside needs to go up enough so I can stand being out there long enough to see if mine needs replacing :)

Air flow is up
Temps are going down

Welcome to WINTER