A vapor barrier or moisture barrier is basically a giant plastic covering that is laid down on the entire surface of the floor and is also stapled to the seams of the walls. This will prevent any moisture from rising from your crawlspace into your home. If the ground moisture is not contained, it will promote the growth of mold and fungi causing bad smells to formulate in your crawlspace, which eventually seeps through the entire house. If your crawl space feels humid or has an awful odor, moisture from the uncovered earth is a likely culprit. A crawl space that does not have a vapor barrier installed is considered unfinished and can lead to problems such as mold growth, dust mites, dry rot, bugs, and critters. A dirt floor is a breeding ground for moisture, termites, and mold.