Hi Ryan, I'm not an expert on this, but I had to study this subject when I insulated my exterior walls. There is a nationally known expert named Lsburick (sp?) who has a book called Moisture Control in Small Buildings. I only read the chapters that concerned my situation. He said it is important to have a moisture barrier in either a cold or warm climate to keep insullation dry. I finally used icynene, that acts as a vapor barrier, because I couldn't get a barrier any other way (removing siding). I'm in the hot part of TX and my vapor barrier goes on the outside of the insulation. If you are in a cold climate the vapor barrier goes on the inside. I found that some wallpapers have a low perm rating and can function as a vapor barrier. I didn't look into that much furter since it didn't apply to me, but I would guess that I would be wallpaper with some plastic in it.