Passive, in-door or through wall (non-insulated) return air pathway and vent for electronic cabinets, utility closets and bathrooms. Honeycomb is for sound dampening and reduce air hiss - you may be able to find/use cardboard honeycomb inserts instead... Print SideA and SideB, sandwich the honeycomb insert between the two. Double sided tape was used on the inside of the flange to mount to the door. You may need multiple units depending on the amount of air-flow needed for the space used - scale as needed. Angled louvers are included if you prefer to use those. This was sized for a door with a depth of 1 1/3" (~35mm).