I have spoken, written, talked, videoed (?) on this topic for years now and yet I still find this stuff behind dryers. The stuff I speak of is white vinyl dryer ducting or more correctly, transition hose. At some point in history, say the 90’s, for some reason this stuff started to get used to connect dryers to the homes ridged dryer vent thus the reason it is called a transition hose. The problem that occurs is the duct is made of vinyl, a material not known for its heat resistance and as shown in the top photo, easily crushed.
Now I know anyone with some time on their hands can do a quick Google search and find this stuff for sale all over the place. And yes, it is out there, but it is meant to be used for air vents. Like the one in your bathroom. A trip up into your attic and you may find this stuff in your own home connecting vent fans to exterior vent covers which is perfectly fine. But once you put some heat to these, they begin to discolor and become brittle. Then add the ease of crushing and then the airflow begins to slow.
Slow airflow is why lint from the dryer gets deposited inside the dryer ducting, exactly where we don’t want it to be because it is easily ignitable. So add all these factors together and we have a product that offers poor performance, is easily crushed, holds onto flammable material like candy, and when subjected to an ignition source will gladly go up in flames. Now that is not something you should want anywhere near your home or family.
The good news is this is an easy and inexpensive fix. Throw it away. Go to your favorite big box hardware store and buy something that says UL listed on it. Must of that stuff is garbage too in my personal opinion, but at least should a fire start in the dryer or the dryer ducting, it will at least give you some time to resolve the issue. All the more reason to get rid of the old white vinyl. And please don’t start the dryer and leave your home or go to bed. I need you around to keep reading this stuff.