Polyester String Reinforced Polyethylene
sheeting is the industry standard for use as a vapor retarder or vapor barrier when one is trying to waterproof, or reduce moisture, radon, methane, or VOC levels entering a home or any other structure from a crawlspace or basement.
The reinforced products come in a variety of types, and one should make sure that any product used in this application has been extrusion laminated. This is a method of joining together the layers of polyethylene (or other types of plastic) with the scrim reinforcement layer(s), where molten polyethylene is used, along with a lot of pressure. The resulting product is very strong, and has amazing tear resistance compared to most types of polyethylene films. Cheaper versions of the reinforced films also find their way into the US market, ones that are joined together with glue, for instance, or heat laminated. Up to this point in time, we do not know of any of these types of products doing very well in this particular application, because of the demands of the application. At this time, we recommend against using any reinforced products that are laminated using such things as glues. Definitely stick with extrusion laminated films if using reinforced films in this application in my opinion.
Why are the string reinforced films the most popular, and are they the best for basements and crawlspaces? First, when this industry was getting going, one product on the market was by far the most popular, right out of the chute. This was a 7 layer extrusion lamination, with two layers of the string reinforcement, officially 16 mil, but mostly marketed as a 20 mil to the end users, as it is to this day. A number of companies went to work marketing this material, and several similar ones, and they really caught on. For the most part, they have simply dominated the market since, mostly because the companies who control most of the market continue to use these products, and have gotten some degree of exclusivity on some of them.
The scrim reinforced films are quite appropriate for this application, and serve the purpose very well. Depending on the needs of the application, there are now engineered films that are actually better choices. Because of breakthroughs in polymer technology, it is now possible to make a polyethylene film that blocks virtually all of the extremely small particle gasses, like Radon, Methane, and many VOC's, along with water vapor molecules. While the scrim reinforced films reduce the amount of these gasses that get through, they are not nearly as effective as this new technology in this regard.
To date, our VaporBlock 20 Plus is the only product we know about on the market with the capability to block Radon, Methane and VOC's. Our engineers claim that it is over 50 times less permeable than typical high performance vapor retarders against Radon, Methane, and harmful VOC's.
The puncture resistance of this product exceeds any of the string reinforced films we know about on the market today. The string reinforcement can actually act like little knives if force is applied to the face of the film, allowing the scrim to cut into the surrounding poly, lessening its strength and vapor barrier qualities or allowing for a puncture where the VaporBlock 20 Plus would not have been punctured at all.
The reinforced films were designed more for covering applications than lining applications. While they have become hugely popular as liners in a large number of applications, their most outstanding quality is their ability to withstand winds, and keep punctures from continuing to tear. My prediction is that over the coming years, we will see a big movement toward this new technology. I can easily see homebuilders offering this kind of liner as standard fare, or at least an upgrade to the standard vapor retarder. This will offer their customers a better choice, and help mitigate lawsuits for mold and other moisture and health related issues. These lawsuits have become almost epidemic since most insurance companies quit covering anything mold related, unless it is the result of an active leak. I think this is very cheap insurance against the havoc that can be wreaked by moisture, not to mention the health risks associated with Radon, Methane, and VOC's.