Dryer vent/ducting

Hi all,
Does anybody here have any first hand experience with periscope type duct that is square in shape,and measures 2" x 6" for limited space installations, and is said to work as well as the standard 4" round duct?

Thanks to all!

 

ALthough they are a little flimsy, they seem to work ok. I have not seen any actual test results about air flow. Be sure to tape all joints with foil tape, or you will "leak" lint.

 

The only ducting I am aware of the should be avoided is the flexible tubing. That's because the ridges inside catch lint and eventually create a fire hazard.

 

We have sold them for years with never a problem. Do tape the joints.

 

Does that hold true if I use about 4' of the flexible aluminum(?) stuff to make a connection to rigid dryer tubing. It was used to simply a sort of complex bend and make connection to the dryer easier. Most of it will eventually be buried behind a finished wall, I'm guessing it should be replaced with rigid pipe. Sorry for the intrusion...