Picture says 1000 words, see the picture attached. This was after about 2 months of the filter being in the AC, next to a freshly cut piece to replace it. Generally they will last much longer but I live on a main road, and a lot of dirt is kicked up by passing cars which contributes to the filter becoming so dark and needing a replacement quickly. It also does a good job filtering the occasional smoke(from cooking or other). These things certainly do a good job filtering the air cycling through window AC units. I cut it to size and attach it to the plastic filter found in the unit with some tape. I dont recommend wrapping it so the filter covers both sides, I did that at first and it significantly disrupts the ability for the AC to cycle air and can hurt the motor long term/cause it to lock/freeze up. But even with the filter only on one side it does a great job. Previously we only used an air purifier, but with these in addition to the purifier I feel confident the air circulating in my apartment is NOW much cleaner.I got these filters to put into the 2 Window AC units I have in my apartment for the upcoming season. I live in NJ and put the window AC units in about 2-3 weeks ago when we had weather of 70+ for about a week straight because the heat in our apartment, which I have no control over was still on, making the apartments extremely hot. My wife also gets extremely bad seasonal allergies every Spring from Mid April through Mid June, so much so that last year we got a purifier in an attempt to help combat the allergies. While the purifier may have helped some, it didnt completely solve our issues, and my wife still has bad allergies so this was the next step, I figured id go with the best, Filtrete over other companies and being branded as Allergen filters it was a no brainer.I do feel as though these have helped probably about the same as the purifier itself did. Its not a fix all, my wife still does have allergies that bother her, but they do seem less frequent and less severe when they do occur. This is of course dependent on the AC unit running so that the filter is being used, if the AC is idle, not air is going through the filter.For the price of these filters, theyre easily the best bang for your buck to help fight allergies and other air impurities if you have a Window AC unit. Also, I thought that 1 Pack would only be enough for 1 filter, but I was actually able to cut one pack, and cover both of the plastic pre-made window AC filters with these filters, AND have some left over which should be enough to cover the smaller of the two filters again. Its also worth noting that there arent very good instructions on using these, it would make the most sense to me to wrap it around the plastic filter most units have entirely, but as it restricts air flow it could cause the AC unit to burn out, and the instructions make it seem as though you should only cover one side. Another suggestion, THOROUGHLY CLEAN YOUR PLASTICFILTERS BEFORE APPLYING. Use warm water and soap, or whatever allergen cleaning method you have to completely clean the filters that come with your units before placing these on the units. Its well known that the filters that come with window AC units are notoriously bad, and if pollen or other allergenic material get stuck in them, they just keep being pushed out into the air which is NOT what you want. It is also very much worth it to get air conditioner weatherseal so there are no gaps between your Window AC and the window itself which could allow air/allergenic material/bugs in. This is crucial to get the best overall benefit from these filters.Overall, I strongly suggest these air filters for window AC units. As I said, in my opinion(no scientific proof) they had about as much an impact on indoor air quality as adding a purifier to my bedroom(which runs 24/7) and the filters are FAR CHEAPER. These are a must have for those who suffer from allergies and dont have central air with filtration.