I have a question which I havent been able to find an answer for….I recently swaped out my dryer vent to 4inch round and went through the cinder block wall. Of course the rough in for the pipe would be ideal to be sprayed with canned foam like Dow’s Great Stuff…However I’m unable to find any documentation as whether its safe to use foam sprayed on or around vent pipe used for dryers as
they are transfering more heat than your typical supply run for for forced air.  Is this something I need to be concerned about? I would be using a canned  closed cell foam like Great Stuff by Dow.