I am not trying to start an arguement here but I have a valid concern over the way I have been connecting dryers . If it is not safe I want to fix it. Each dryer is connected with one to three feet of aluminum flex to the hard pipe in the wall. It is the same stuff you describe with the slinky inside. Now I went out to the shed where there is a plastic bag containing “deflect-o” brand 4" flexible aluminum “air duct”. It does state on the bag “Not recomended for dryer venting”. It is 25 feet long. This is what I use for venting bathroon fans with 4" exhaust fittings.
Then there are some boxes from Ace Hardware that say “Flexible aluminum dryer vent duct” The stuff inside looks the same as the kind in the bag. The one in the box is made in the US, the bag comes from Canada. The box says "UL listed, but it doesn’t say for what it is listed. It is only five feet long. This is what I use for dryer venting transitions. Again, it it called “Dryer vent duct” on the box.
The corregated pipe you refer to, if it is what I am picturing, does not have a smooth interior surface. It is made up of aluminum in a spiral shape with grooves and ridges on the inside. It comes compressed and you stretch it out. The piece I have has no label.
So I guess the part I don’t understand is what I should actually be using for the transition. Is there a product that is flexible AND has a smooth interior surface?
Excuse me if I sound ignorant, I am just trying to learn. I am the type of person that insists on doing a job 100% correct.