Why Closed Cell Foam?

Homeowners sometimes aren't savvy to foundation contractor's small tricks to save a buck. Here's a giant for you! Many foundation contractors have begun using spray foam as a way to put a few extra dollars in their pockets, nothing wrong with that, or is it? It's worth mentioning here that there are two totally different types of foam insulation; the first is "open cell" and the latter is "closed cell" and one is a good bit more expensive and works great for crawl spaces the other is less expensive and should never be used in a crawl space. Why do I see the cheaper of the two more often then not? Could it be that the contractor chooses the wrong one because they look similar? An innocent mistake? Or is there a more sinister reason at work here? Anyway I'd advise any homeowner considering spray foam for their crawl space to really do their homework and question their contractor about his/her choice in foam and then insist on "closed cell" be used. Here's several microscopic looks at the differences and I believe at a glance the average newly, just married, first-time homeowner can figure out as to why the cheaper is not better...