Product review (4 stars): Hey Broan CEO, Read This To Improve Your Products
Solid, high quality steel vent cap.  Much better build than the tinfoil ones in the big box stores.  I dinged one star because, like others have noted, Broan's quality control is lacking as you will need to adjust and add a bit of weatherstripping foam to make the flapper seal airtight.  For the price of this product, I should not have to do the finish work.  As modified, flapper seats properly and seals out the cold.  Had the same issue, but only worse, with Broan's 3 1/4 x 10 inch wall cap, where three sides of the flapper were missing foam.  If I were the foam strip applier at Broan, I'd start packing my stuff and handing my resum out.