Product review (4 stars): Seems to do what it is suppose to do...
I had a straight vented pipe with an aluminum shield on the outside of the house.  There was a little flapper just beneath the shield, but it was busted and stuck in the open position.  The metal vent pipe going up the wall from the base of the dryer and out the side of the house used to get so cold that moisture would condense on it and I would feel the cold air just blowing in beneath the dryer and out from the drum when I had the dryer door open.  I bought this item, hoping that it would better insulate my dryer vent from the cold and it seems to do what it is suppose to do.  I have reached over the dryer and felt the pipe a few times and it's cold, but not the freezing cold that it used to be; plus I don't seem to feel the cold air at my feet like I did last year when I was doing the laundry.  So far, so good.