This is for 3D printer enclosures that have an exhaust fan wired to a temperature triggered relay. It is compatible with any fan up to 140mmx140mm. These louvers are designed to open upward, so the fan must be mounted above the louvers. The louvers will help contain heat until the fan turns on, which will lift the louvers as it exhausts heat. The louvers will close again when the fan turns off.
This design also incorporates a slot at the top for an activated carbon filter pad. This will help prevent toxic fumes, such as styrene from ABS, and smells from escaping the enclosure.
I use this filter pad cut to the appropriate size, but any filter pad up to 1 inch thick will work:
https://www.ebay.com/itm/Activated-Carbon-Filter-Media-Pad-Aquarium-Pond-Filter-Media-Canister-Foam-Sheet/254458720543?hash=item3b3eebf11f:g:IhsAAOSwlj9eAbOE

You will need 4 Small Louvers and 1 Big Louver for the Exhaust Louver Base. The Big Louver has a flat face and and that face will go at the end against the wall of the base. Assembly should be obvious once the printed parts are in front of you. Just bend the louvers in the middle to get their pins into the mounting holes. Make sure the pins and holes are cleaned up so they rotate smoothly in the holes.

The enclosure will need vent holes in it for air flow when the exhaust fan turns on. Otherwise the fan wont be doing anything but spinning and it wont lift the louvers. Drill some holes near the bottom of the enclosure for ventilation and use the Vent Louver Base and a Big Louver to cover the vent holes. I recommend using six vent holes in total. Drill 3 holes, 1/2" or 12-13mm in diameter, close together and cover with one Vent Louver Base + Big Louver. Do the same thing with the other 3 holes.

If you print any of these parts in PLA, they will warp from the rising heat. Use PETG at least, or better yet, ABS.