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What Is a Vapor Barrier

Vapor barrier is a term used to describe a material that protects from moisture or water vapor. This can be many things to many different people, but for the purpose of this site,  vapor barrier will refer to polyethylene film or “plastic sheeting” as it is also called.

In the polyethylene film industry there are many quality grades, sizes and colors available. The best vapor barrier for each application will be determined by the requirements necessary to achieve the desired results.

Vapor Barrier Types for the Crawl Space

Ingredients

The quality of ingredients used to manufacture a vapor barrier can range from low grade, made with recycled plastic (water bottles, used vapor barrier, etc.) to high grade that is made entirely from virgin polyethylene resin and of course every variation in between made by mixing both recycled plastic and virgin resin. Longevity, that is the difference between vapor barrier made with recycled plastic and vapor barrier made with virgin resins. The more recycled plastic a vapor barrier has, the quicker it will break down, become brittle and fail while vapor barriers made entirely from virgin resins will last nearly indefinitely in the same indoor environment.

Method

Manufacturers of vapor barriers also offer a wide range of quality. In an industry where the consumer demand is for “cheap” rather than for high quality leaves a vast distance between both ends of the quality spectrum. In some cases one has to only look at the vapor barrier to tell it is made to be cheap, but that is not always the case. In fact, visual inspection is the least reliable way to determine the quality of a vapor barrier. There is very little concern for quality if the vapor barrier is going to be used as a “drop cloth” on a bedroom painting project. However, the quality is of the most important if the vapor barrier is going to be used under a concrete floor in a high end shopping mall.

All polyethylene film can be tested to determine performance expectations. Although testing methods like ASTM will not determine how much recycled plastic is in the vapor barrier, it will show testing results that are consistent with vapor barrier made with either virgin resin, recycle plastic or a mixture of both.

Reputation

Unless you are building that high end shopping mall, chances are you will not take different kinds of vapor barrier and have them all tested to make sure you get a good one. So how do you know? One of the first things you can do is to ask for the products ASTM testing results or product sheet, as it is more commonly called, for the vapor barrier you wish to purchase. Reputable companies will share this with you easily. In contrast, be aware of companies that do not have these results or will not share them. Unfortunately, in the polyethylene film industry, there is little done to stop companies from supplying false information on their product sheets in order to qualify for projects with strict requirements. Once these companies have forged the needed documents, they will also use them to build confidence in their products on the retail market as well, so buy from a company that has a good reputation.

Lastly, ask the right questions. You will find companies that state their products are made from virgin polyethylene resin, however what they won’t tell you is how much of their product is made from virgin resin. What I mean is, a vapor barrier that is made from using 50% recycled plastic and 50% virgin resin is still, technically, “made from virgin polyethylene resin”. The way they stated it makes anyone think it is made using 100% virgin resin. So make sure you ask the right questions, those type of companies won’t offer it on their own.

Cost

Vapor barriers made from recycled plastic is far cheaper to make than vapor barriers made from virgin resin. Know what you are paying for. As much as you don’t want to pay the price for virgin resin and get recycled plastic, you should not expect to get virgin resin for the price of recycled plastic.