 And I was wondering if a person needs a vapor barrier behind there. Yeah, there are a lot of advantages to spray foam insulation, and one of them is that you don't need a vapor barrier. The concept of managing moisture with a spray foam application is not the same as if you had fiberglass. You need a vapor barrier in a fiberglass situation because you need to keep the moisture from building up in the fiberglass and making the insulation ineffective.