Which way should furnace filter face?
Better quality filters generally will be directional. This is due to the filter containing a coarse and fine media or one side being reinforced with wire or mesh to support the filter against the flow of air. It may also be designed to flow air better in one direction. If you can feel or see a density difference between sides the least dense side should face out If the filter is not labeled it should install in either direction as there is likely no difference  from one side to the other