I assume non foil flashing tape will suffice? My local store has a bunch of 3M flashing tape, non foil I think.

After looking at my set up, I'm not sure if the stick foam would fit around the vent without impeding it. Unless I found some thinner stuff. But I'll poke around.

Thanks for all the helpful response folks. I really appreciate them.

Spent some time last night researching different insulation brands / types. Come to find out, I have this in my basement. GE Insulation Foam

The previous owners left a good amount of similar cleaning & gardening supplies, and a bunch of paint cans. The spray can is not that old either, it has a production date on it.

Unless this brand is complete garbage, I guess I'll use this around the interior vent. I'll have to get some sealant for around the vent's exterior myself. Can't find everything in the basement I suppose.

It does seem that way.

Yeah the microwave itself is new that I'm putting in. But there was an older microwave there and the vent was previously installed.

When I took the old one down, that's what I noticed that the vent was basically uninsulated.

You mean changing out the vent itself? I suppose I could look into that. I'll have to see how it's secured in.

I'll look into it.

Yea their is some in the wall, just not right around the vent. It's closer on the sides, but the top and bottom has much more empty space.