Crawl spaces and basements are very similar in structure and both are subject to the same environmental influences such as groundwater and vapor diffusion. For this reason your strategy for insulating a basement must appropriately address the environment. If we are insulating the crawl space walls we will use nothing other than closed cell spray foam as it extends below grade and must be able to effectively deal with moisture. If we are insulating the underside of the floor above and have sufficient clearance we will give you the option of using open cell foam which is much cheaper provided you have a vapor barrier installed to protect it from moisture penetration. That being said however we do recommend closed cell foam if the budget permits but open cell foam if installed properly with a vapor barrier will perform very well in this environment.