Product review (4 stars): Wosk ok, even good, but could be better
did what I expected - a little disappointed in that the gaps around the vertical hinge pin allow maybe 10% of the back draft through.  Still a vast improvement on the situation. I used this device in our dryer vent. WE share a common dryer vent manifold with 2 condos above and another 2 below. When others crank up their dryer, we were getting backflow into our condo.