Originally Posted by
fc321
Im starting to consider the idea of cutting away the outer border of a used filter and staple a few over-lapping coffee filters. This should kept the debris out but it wont help with the foul smells. But you can prevent "stinking" a/c vents by remembering to turn off the snowflake (on the air conditioner) a few blocks away from home and let the vents dry out with dry air. Its the wet droplets left behind in the a/c vents that grows the mold and bacteria that is responsible for the foul smells.
Actually if we are just looking for a "screen" then maybe a combination of window screen + coffee filter? Or how about a piece of cotton T-shirt?