Product review (5 stars): Works well for me
This wall cap is at the end of 4" duct work connected to an upstairs bathroom fan in my house, and does its job well. It comes with aluminum tubing, but if you're going to be running your own rigid duct work, which I would recommend over flex stuff, remove the tube that comes with this wall cap and throw it out. The spring-loaded damper does its job well, and doesn't appear to flap in the wind when the fan is off. I painted this cap to match the color of my siding, too, in case anyone was looking to do the same. The paint stuck very well.