insulating dryer vent against condensation

So I am in the process of insulating the concrete basement walls with EPS boards, and will also put some EPS board in the joist area and spray some foam the cracks/joints to stop leaks.

in one corner of the basement I have a dryer vent going through the wall to the outside.

the vent is 4" round galvanized steel, and it is going through the joist area (first through wood then through brick).

the gap between the metal duct and the brick/wood was sealed with expanding foam insulation.

It is now cold out (about -8C/17F) and while doing my insulation work I noticed the first inch or so of the metal duct, when it comes out the wall, is very cold and moisture is condensating on it. this is basically about 10 inches away from the outside.

the vent I have is like this: http://www.homedepot.ca/product/progard-vent-hood-white-4-inch/963996

it basically has some louvers on the outside that close, but it's not exactly leak proof so cold air from the outside is going in the duct and making it cold.

this duct will eventually be in the ceiling/wall, and obviously I don't want moisture on it in winter, that could cause problems long term.

so how an I insulate this pipe so that moisture doesn't condensate on it anymore?

I thought about spraying foam on it on the outside, which would prevent any humidity from touching the duct, but I am concerned about the foam self igniting if the vent gets too hot. is this a valid concern? if so, what about the 10 inches or so inside the wall, which are already filled with foam?

any other ways of insulating this to prevent condensation?

the air inside the pipe will always be cold anyway, so what I think is important is to prevent moisture from touching the duct. so then just putting something like fiberglass batting on it would not do anything, since moisture can still go through, right?

Submitted November 29, 2014 at 10:48PM by JeNiqueTaMere http://www.reddit.com/r/DIY/comments/2nrpd0/insulating_dryer_vent_against_condensation/