I recently stayed in an apartment that didnt have central air so I created a corsi-rosenthal box since the smoke from the Canadian wildfires were so bad.
After 30 days of continuous use, with very minimal periods of it being turned off, this is what the filters look like!
It's disgusting yet also so satisfying to see the filters get darker from debris, dust, and dirt.
Edit: typos
You just cut the tape off. They last a pretty long time. I've got one going for two years intermittently here. If it looks too rough, you can take it out side and use a vacuum or air compressor to remove a lot of the surface dust.
Tape on the bottom is for the bottom panel. Usually it's just a cardboard sheet.