Product review (4 stars): Product as described
Decently heavy plastic construction

I don't recall seeing a description of how these function so I will mention it.  The outer cylinder is just a housing that allows the exhaust to go through the bottom.  Inside the cylinder there is a smaller diameter pipe the has a floating cap on it.  When the dryer exhaust pushes on it, it rises and lets the exhaust escape (easily).  This floating cap is contained by the outer cylinder so as not to come off.  Without the exhaust pressure, the inner cap just floats down over the inner pipe (gravity) and provides a closed end.

Definitely of sturdier construction than basic wedge shaped dryer vents with flappers.