Product review (1 stars): Our plumber did not consider this to be a dryer vent
This came packaged simply in a plastic bag with a small bar code sticker. It was certainly strong if not quite to the point that you could beat on it with a hammer. The pipe had an open seam so that it tapered from 3 7/8" to about 3 1/2".  Unfortunately, there were no instructions. We thought of two ways to install it. You could slide it into a standard 4" vent pipe; however, it will be loose and will tend to catch lint at the joint. You could stretch and slide this over a 4" pipe; however, it wasn't clear how to do this. When our own attempts to install failed, we talked to several plumbers/professional installers, none of whom seen anything like this before. Their main concerns were as follows: no flap to prevent incursion of hot/cold air; the large holes in the grill may allow insects to enter, e.g., wasps could nest; and the grill will trap dryer lint and will require periodic cleaning (it pivots up for this purpose). We were discouraged from using another and common style of dryer vent with four flaps since these can also trap lint. We finally had someone install a product similar to the "P-tec Products Inc NPVT No-Pest Vent" which is cheaper and whose design avoids the concerns raised about the Forever Cap.