Air Infiltration Around the Dryer Vent

Now I need to decide what to do around the dryer vent. Our dryer is immediately off the kitchen. It's right next to an exterior wall, so the vent has a very short run. However, this configuration allows a LOT of air leakage:


One option is to seal around the orifice with the appropriate insulating material. But what? The foam-in-a-can stuff is combustible above 240 degrees fahrenheit; I'm reading that the high setting on a clothes dryer approaches 350 degrees. Another option involves this contraption:

I know very little about it, other than its supporting webpage.

The blogger at Dover Projects provided a thoughtful post on the same subject. A similar discussion is on Green Talk.

[Post script: I eventually installed one of these; the story is here.]