Insulating dryer duct?

Maybe, but that's not as important as 2)

Yes, if you do the following: Louvers are to keep out the weather. In addition your vent must have a self closing flap such as are used on range hoods. Further, you will gain something by insulating the metal panel in the window. Do all that and you likely save a few $$.

Joe

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Yes! I put one of these on a few years ago and am impressed with how well they work-

How do you clean them?

work-

The lid is hinged & you can get to the guts.

Jim

Without a doubt add a louvered exhaust or other kind of back flow preventer.

Insulating the pipe will mean the the pipe will get much warmer when the dryer is running. This is good. It will tend to keep the pipe/duct void of condensation and the lint won't stick to it as easy.

Any suggestions on type of insulation? (safe, effective, professional looking)

Looks like a neat contraption... but my vent is through a basement window pane (actually the window is 3x1 and one of the panes has been replaced with sheet metal containing an integrated vent).

Not sure how/if this would be installed in a window without some customization...

If needed you can use flex duct casing or fiberglass. Mine was very cold, but temperatures are now 10-20 warmer.

You might want to try another exterior dryer vent. The flaps will slow down the cold air movement, yet light enough to allow easy airflow.

I also using one of these. Works great and easy to clean IF needed. WW

You could just leave it alone. Without a flap, eventually some critter will make a nest in the duct, effectively sealing it against further air intrusion.

Thats what I have, I know of no other system like it.

I'm not sure what to suggest, I'd have to scan the insulation isle at the depot and lowes. I'm wondering if it would do good inside an insulated flexible AC/Heating duct, although I doubt it's code. You could probably put it inside 6" duct.