Activated carbon cabin filter: carbon side up or down?

In my admittedly minority opinion, it does not matter. A wet hankie would do fine.

But, the air flow comes from the fan. In the gen II the fan is down toward the floor. Don't know about your Gen III, but the Gen II fan "PULLS" the air from the outside and "down" into the car.

If the Gen III is like the Gen II, the air flow is toward the pavement (down). So, your arrow, if the Gen III is the same, would point to the road, or toward the fan.

 

Thanks. It does appear to be sitting directly on top of a fan

 

in a normal stand-alone household indoor Hepa Air Filter / fan, there are two pieces in the filter system, a carbon pre-filter sheet, and a HEPA folded-paper filter. The reason is that the pre-filter sheet gets gummed up with dust, hair, lint, etc, but it's just a sheet of scratchy fuzzy stuff that you cut out with scissors to shape and install in the machine, and it can be replaced cheaply and frequently (or even cleaned), so the more expensive HEPA filter can stay cleaner longer, get replaced less often, and take care of the fine particles.

since these car filters are one piece it seems like its irrelevant, you dont have the option to "just replace the pre-filter".

makes me wonder if i could cut out a sheet of pre-filter from my householder filter and jam it into the cabin filter tray somehow...

 

It might be a little clumsy and possibly fold over, unless you attach it to the filter somehow.

moto g(7) power ?