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The Magnetic vent filter is a soft PVC grid device with a washable poly propylene mesh media filter. The filter is placed over a forced air HVAC room vents and cold air returns when placed over vents, the filter will prevent most dirt, dust and airborne particles that may enter the ducts from coming back into the room. They can be placed over cold air returns where it will reduce the amount of dirt that's pulled into the HVAC system as well as bathroom exhaust fans. I got one and it really helps . You can get them here 

https://www.amazon.com/gp/aw/d/B01AIQM4VI/ref=mp_s_a_1_1?qid=1455757483&sr=8-1&pi=AC_SX236_SY340_QL65&keywords=tidydocks+air+vents #tidydocks