Some things are designed to be thrown away. That Styrofoam container you got with your takeout order? Trash it! But that plastic container you saved last night’s pasta in? That one can be reused time and time again.
Air filters that work with your home’s air conditioning system are the same way. There are some filters designed for only one use (although “one use” is about a month). Others can be used time and over and over—as long as you keep them clean.