All About Vapor Barriers


Definition of “Vapor Barrier”- A Class I vapor retarder

Class I

Less than or equal to 0.1 perm
•Aluminum Foil

Class II

Greater than 0.1 perm but less than or equal to 1.0 perm
•Kraft Faced Insulation

Class III

Greater than 1.0 perm but less than or equal to 10 perm
•Latex Paint

12 Mil Crawl Space Vapor Barrier

Since a 20 Mil vapor barrier is the most sought after; Why would anyone offer a 12 Mil crawl space vapor barrier? We went to CrawlSpace Concepts to get the answer. "The simplest answer, we needed something comparable to those 20 Mil crawl space vapor barriers on the market. Even though our 20 Mil was similar in price to the 14 Mil vapor barriers that were being called a 20 Mil, we felt we should offer a product that gave similar results at a much more reasonable price." states Matt Leech, President & CEO. "The truth is, a 12 Mil vapor barrier for your crawl space is plenty strong enough as long as you don't have special conditions that require something tougher."

So what is the break down on the 12 Mil products? You guessed it, a wide variation of what companies call a 12 Mil. The SilverBack™ comes in at 60 MSF (pounds per 1000 sq ft), while at the other end the NT-1200 weighs in at only 38 MSF.

Truth in advertising is spread thin, literally...

20 Mil Crawl Space Vapor Barrier

20 vapor barriers are the most sought after thickness for crawl space encapsulation. While most of these crawl space vapor barriers claim to be 20 Mils thick (.020 inches) they actually fall short if you were to measure the actual plastic. To get the most bang for THEIR buck they measure the vapor barrier at the thickest point; that would be on top of the string reinforcement. Some measure where the strings cross in order to cut the amount of plastic used in the film and still show 20 Mil in their pictures.

A true 20 Mil crawl space vapor barrier is about half as thick as a dime. The best way to identify a true thickness 20 Mil vapor barrier is to look at the products weight. In the polyethylene film industry the weight is measured in pounds per 1000 square feet or MSF. A true 20 Mil will weigh in at about 109 MSF, thats about 5 pounds of plastic per Mil. Besides the SilverBack™, some of the other brands on the market like CleanSpace™ weighs in at 83 MSF and NT 2000 at 74 MSF. The 20 Mil SilverBack™ weighs in at 109 MSF. In fact, Mr Leech says that is why the largest roll of 20 Mil SliverBack™ is only 90' long because it is to heavy for UPS to deliver at 100' or 151 pounds.

So, does it really matter if you only get 14 Mil of vapor barrier when you pay for a 20 Mil? CrawlSpace Concepts, the maker of the SilverBack™ crawl space vapor barrier, thinks so. "Most of these brand owners hope you won't check the thickness. So, what you dont know won't hurt." says CrawlSpace Concepts General Manager, Mike Leech. "The real injustice is, the company only delivers 70% of what the customer paid for. In what other industry can a company get away with that? Could you imagine buying ten 2x4's at the home improvement center and only leaving with seven?"

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