Magnetic with the worst strength in magnets you can find. Literally because there are little fans, it doesn't slide down. You put the glue wherever you want and start. Otherwise, it does what it should to a very good degree. The dust stays out of your box. BUT... in my case, sometimes the fabric sticks to the little fan and you can hear the sound of rubbing. They haven't been placed incorrectly.

The filter is magnetic, but in the package there is also a square frame which on one side sticks to any surface (it contains glue) and on the other side magnetizes the filter! It can be placed practically anywhere.