The definition of antimicrobial according to Wikipedia.org-

"An antimicrobial is a substance that kills or inhibits the growth of microorganisms[1] such as bacteria, fungi, or protozoans."

It is a cheap additive to a crawl space vapor barrier and an ingenious marketing scam. The truth is; mold, mildew and fungus need an organic food source to grow. Polyethylene, polypropylene, PVC and other plastics are not made from an organic source, therefore are not food for fungus's like mold and mildew. This means mold will not grow on the plastic unless an organic material has been added to the plastic. Polyethylene is used in many water and moisture containment products all over the world without an antimicrobial additive. I must admit that in the crawl space world, offering a product that implies you will never have mold in your crawl space because the vapor barrier has an "antimicrobial" in it, sounds great. So I researched it quite a while ago. Here's what I found; Most antimicrobial are designed and marketed to protect and kill bacteria on the skin, like soap, and to protect our clothes from smelling dirty (after one wearing) by adding it to the fabric itself. The purpose is to kill the bacteria that lives on our skin causing body odor. It is also used in cat litter, pillows and baby wipes. So the question remains, will it prevent mold growth in the crawl space? The answer is NO. It will keep mold from growing on the vapor barrier, but mold wont grow there anyway. And the whole purpose of making the investment in your crawl space is to keep the moisture levels down below 55% so mold cant grow at all. I know for sure that the antimicrobial additive in the vapor barrier will not stop mold growth on your wood structure, which by the way is an organic food source and more likely to have a problem with mold.

So maybe your thinking, what about mold growing under the crawl space vapor barrier? After all, there is going to be a lot of moisture there. My answer to that is, if the crawl space is properly prepared and cleaned out there will not be any food under the vapor barrier either. An antimicrobial is not needed as a vapor barrier additive in plastic to prevent mold growth. If it were, plastic would not be a good product to use in a crawl space or as a vapor barrier period. It all comes down to marketing, product sales and money.