[solarhotairpanels]

You're very welcome Exeric,

What's cool about this type of damper is it can be customized on the fly as in sized to any duct size and configuration of ductwork.. or just used to stop drafts in certain areas of your home / shop etc.

round / square.. it doesn't matter as long as the material you use is long enough so after it collapses it just flops flat, sealing the opening.

The ones I made were sized and inserted into 6 inch round pipe.
The material must be suit coat lining type material or something very similar because you can't hardly blow air thru it yet it's so flimsy it collapses immediately flat as a pancake when fan shuts down.

I used plastic For Sale Sign material to create the custom sized tube because it's water proof.

Make sure when constructing your tubes that they are long enough (say 7 to 8 inches) so they do not 'roll over' inside your 6 inch pipe when the fan turns on. There's a lot of vacum inside the return pipe when fan turns on.

I have forced hot air heat at my house.
1 air handler unit is in my attic so I'm going to build one for the 'return' filter register which is 2ft x 2 ft square and located in my 'ceiling' of all places.

When the heat is on the material will lift straight up into the air..
When the heat dies, it'll flop down over the opening to stop any unwated drafts coming back thru the 'return' from my attic air handler.

I'll have to get creative with this one though and use string to stop the cloth from opening 100% when the heat is running cuz I want to make sure the cloth collapses 'in on itself' when the fan turns off.

so great. I'm glad you liked my little kick butt damper.

The ones I've installed at my house are doing a killer job.

I even built one with double layer of material just to see if the double layer of material would allow it to open all the way and it not only opened FULL OPEN when fan was ON but collapsed completely after fan off making even a better seal.

so consider using a double layer of fabric for better insulater when wrapping your custom made plastic tubes.

Just more info here..
for 6 inch round pipe dampers you would want to cut the material 20 inches x 24 inches to wrap around the tube if you are going with a single layer of material. About 2 inches of that material will be overlapped when taping it to the tube.

When you are done taping it to the tube and pushing the cloth back thru the tube you'll have about 12 inches of material sticking out the end of the tube which is the part of the cloth that collapses with fan off.

If you don't leave at least 12 inches sticking out of the tube you won't have enough cloth there to block the opening after it collapses.

Just to play it safe...
After inserting the damper into the 6 inch return pipe I reached in the hole with a piece of duct tape and taped the bottom of the cloth to the metal pipe to stop the cloth from blowing back the wrong way. Highly doubt that would ever happen but just in case.. I taped it down.

Take care and good luck to everyone on your missions.