Review on Versatile Cut-to-Fit Carbon Pad Pre-Filters for Air Purifiers, Furnace Filters, Trash Cans, and Air Conditioner Filters (1) by Jeremy Camacho

The best thing about these filters is that they don't block or restrict airflow. You can still feel the air flowing through the registers just as strongly as before. The ones I've bought in the past have reduced airflow which puts a strain on the AC system. I cut and attached a filter to each of the A/C registers where the air is blown out. Cut it off an inch or two more than the box size and you can just tuck it in and it will close the whole thing and stay in place. The material was easy to cut with scissors and there was plenty of material so I was able to cover the entire 1000 square feet. meters of residual material. Does it help against odors? Possible, although difficult to verify. This is advertised as a pre-filter, so I think you could use it on the air intake rather than as a post-filter. Just don't do both or it will likely impede airflow.