Arrow on properly installed cabin air filter needs to point up
 

I've noticed that mine was installed with arrow pointing down. It's confusing issue but if you look down in the opening you can usually see the leaves and such on the bottom which is additional proof that air flow comes in from underneath the filter and flows upward. if you look closely and think for a bit, it's clear that arrow up is the proper way.

Mine was last installed by PO at the dealer and I guarantee that some of us here might be running filters backwards. Check yours and be sure.

mines pointing up :)