To get the most out of the SilverBack™ vapor barrier and foundation insulation, be sure to install both correctly. This diagram shows how to install them in your crawl space.
By installing the crawl space liner over the insulation you will prevent holes in the vapor barrier from securing the rigid foam to the wall. It goes without saying that the holes would not be a good thing. The rigid foam will not absorbe moisture. However, please be aware that spray foam is not the same as rigid foam. The spray on version will absorb moisture and that moisture will lower its R value.