Whisker Litter-Robot 3 Carbon Filters, 6-Pack

Thick carbon filter that helps to trap odors. I change the waste bag every 2-3 days, since my cats almost exclusively use the robot. I then change the carbon filter once per month. I used to have the second generation robot and rarely changed the filter. The robot wasn’t big enough and my cats would piss out the front, down the step and into the filter. Gross. The filter constantly stunk. This new robot and set up works great. No cat piss out the front and no nasty filters.

Perfect fit (as one would hope). They certainly do the job and make a difference. I wouldn't recommend changing them as frequently as indicated, though. You can get more life out of them than you would think.