Product review (5 stars): Works great!
During a recent cold-snap (5 degrees), I realized my external dryer vent was letting-in a tremendous amount of cold air. My dryer was so cold, the metal housing of the dryer was radiating freezing cold air into my entire laundry room. I could have made ice-cubes inside the dryer itself. Once it was warm enough, I installed the Heartland dryer vent closure.  Very simple to install, but the metal tube running through my exterior wall seemed to be too large in diameter.  I had to crimp it a bit to make it fit in the dryer vent housing.  However, once it was installed & caulked, it worked like a champ!  No more cold air getting in, and no problem letting dryer air out. I'm impressed.