I have this old build-in AC which never had a functional discharge duct. I want to make short duct or sock, but what is the best material to use?

It has to be airtight, yet still light and flexible to work with. Some kind of nylon?

A watertight fabric would work, but a tarp is too thick and heavy and any plastic like material might make a noise if it is flapping with the air movement.

 

Standard is wire reinforced concertina tube, available from all big outlets often sold for extraction fans. With a long run large diameter PVC is used in the middle.

37 minutes ago, sometimewoodworker said:

Standard is wire reinforced concertina tube, available from all big outlets often sold for extraction fans. With a long run large diameter PVC is used in the middle.

Different application. 

This is just to connect the build-in AC with the discharge point.

 

6 minutes ago, ExpatOilWorker said:

Different application. 

This is just to connect the build-in AC with the discharge point.

 

Water or air?

I'm thinking future board and aluminium tape. Almost as in the picture.

 

 

Comes in sheets from art shops. 3mm,4mm, 6mm

1 hour ago, VocalNeal said:

I'm thinking future board and aluminium tape. Almost as in the picture.

 

 

Comes in sheets from art shops. 3mm,4mm, 6mm

Actually not a bad idea and certainly a step up from the cardboard box paper that was previously used.

 

I will get some of the below fabric and have it made to dimensions. 

 

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I think someone cheaped out your AC. You should have something that looks like this:

 

 

The future board should work as well as the card-board anyway. Duct-board would probably work best. 

21 hours ago, Yellowtail said:

I think someone cheaped out your AC. You should have something that looks like this:

 

 

The future board should work as well as the card-board anyway. Duct-board would probably work best. 

The future board did the job and it is working and looking great. 

The AC is similar to the one in the picture, it is just build into a wooden cabinet and I just needed to direct the exit air to the outlet so it doesn't circulate around inside the cabinet.