The carcboard frame and the material used to enforce the filter are subpar. After several weeks, especially as furnace is used more due to colder weather, they collapse inward and become useless. Doj't waste your money.

My home uses return air filters 20x20 and 24x24. I've been buying 20x20 MPR 300 and 24x24 MPR300. After my last purchase of 24x24 pack I too thought the 'air direction arrow' was backwards by mistake; I called in and was advised that the arrow was indeed correct. I take issue with that, especially on the 24x24 with all the cardboard 'crisscrossing' in addition to the new 'plastic wire' net all on the intake side. That's a lot blockage of air flow. You shouldn't need the cardboard strips and crisscrossiing with the polypropylene net The 20x20 had much less reinforcement so the airflow is much better but the cardboard filter frame comes apart.

This is a low cost Merv 5 (out of 16) filter, I change it about every five weeks during our Colorado heating season. My theory for filter maintenance is to use low cost filters and change theme often. The furnace runs fine (moves plenty of air) with this filter and a 5 week change cycle seems to work well.

Great product. If you have a dog, thus filter works very well.