Changing out the cabin air filters in my 019 991.2 C4GTS. The two UTUBE vids I watched show the airflow direction of the in cabin filter (not the prefilter in the frunk) from passenger (right) to driver (left). However, the one that came out of my car had the airflow arrow opposite (drivers to passenger). Which one is correct? Does it really make much difference?

Vids:

Also bought those Hengst "upgraded" biocide filters from FCP. After installing, would not recommend the one for the frunk. It is very stiff and will not easily slide all the way in. You have to pull it to the bottom to make it seal. If it does not properly bottom out you have a massive air bypass and is like not having a filter in at all.

 

Funny you mentioned this, i also replaced these recently, and thought it was strange that the new Mann filter i got, that installs in the passenger footwell (CUK25006), didnt have arrows printed on it indicating airflow at all, just like in the second video you linked above. I ended up just installing it with the writing on the filter being closer/towards the passenger side, like he stated in the video, and im glad i saw that video now because i thought maybe i got a defective one. In the past though, ive always installed them with the arrows facing the driver side. Its very likely whoever installed yours previously did it incorrectly.

Has anyone else thats ordered this Mann cabin filter recently, got it without arrows printed on it as well? Even the instructions didnt state anywhere to make sure the filter is installed a certain way, based on direction of airflow, and im pretty sure in the past they always did. Also, every Mann filter ive ordered in the past always had the arrows printed on them for airflow, so not sure why they would change this now.

Regarding the cabin filter that goes in the frunk, yes, ive heard many times in the past that only the Mann one installs and bends properly there, and many other owners have had issues similar to what you experienced. Many posts on here stating that the other filter brands' version of the frunk cabin filter (even the premium filter brands like Mahle, Hengst, etc) dont bend properly or install easily, for whatever reason, like the Mann one does. This filter also needs to be installed a certain way, with the words printed on it, facing the passenger side, and arrow or tip of the triangle, facing the rear of the car.

Should be easy for you to return/replace at FCP though.

 

Yes, the "prefilter" in the frunk is critical re flow direction, as that one probably gets the largest particle/dirt loading. The Hengst I bought has a biocide (blue) layer that should be facing inboard. It is very stiff and you actually have to pull and push it down, guiding it all the way to the end stop in the housing.
Regarding the cabin filter inside the car, I suspect its main purpose is fine particle removal along with activated carbon for odors. In that case flow direction is probably not that critical as it would work to remove these contaminants in either flow direction. I used another Hengst here with the blue layer but strange that the blue layer is upstream and not downstream as in the prefilter (based on the arrow flow indicator).