Product review (4 stars): Hey Broan CEO, Read This - You've Brought the Ball to the one yard line, but need to get it OVER the line.
This is a heavy duty wall cap made of thick metal unlike the tinfoil aluminum ones found in the big box stores.  I dinged one star because, like with another Broan 4" round cap I purchased to vent a bathroom fan, the finish guys at the Broan factory need some CMFE (Continuing Metalwork Finishing Education) as both wall caps had mis-aligned and missing insulation.  For this one, there was only foam insulation along the bottom of the wall cap against which the spring-loaded flapper seals (picture a rectangle - only the bottom long side had foam insulation - the left and right sides and top were missing insulation).  Moreover, this single strip of insulation was mis-aligned, so that there was a gap at the end.  If you live where the winters are cold, it's critical for your vent cap flapper to have a tight and complete seal, otherwise cold air entering the microwave could cause frozen condensation to build up inside the microwave.  After removing the bird screening (it's held in by friction) I had to carefully and slowly pull up the insulation strip and re-seat it in the proper place.  Then, I had to make a trip to big orange for some 3/8" wide by 3/16" thick foam insulation, and once applied to the missing three sides, that sucker was sealed up tight when the flapper was down.  In my particular installation, I had to trim back the part that sticks through the wall.  Due to the heavy gauge metal, tin snips were out of the question.  My jig saw with a metal cutting blade made quick work of it, but consider ear protection because cutting flapping metal is not a quiet affair.  Even after MacGuyvering this to my satisfaction, I'd buy it again because of the heavy duty gauge of the metal.  Just be prepared to do Broan's finishing work for them.