What Is the Difference Between a Vapor Barrier and a Plastic Sheet?

If you put a vapor barrier and a white plastic sheet side by side, many might not be able to tell them apart. Although vapor barriers and regular plastic sheets look similar, the material they are made out of makes them very different. It’s because of these differences that the vapor barrier is capable of protecting your basement from water vapor while the plastic sheet cannot. Vapor barriers are made of polyethylene, which is a type of polymer that is molecularly denser than normal plastic. It’s because of this density that vapor barriers are so good at blocking off water vapor, whose particles are incredibly small and difficult to contain.

Polyethylene is among the most durable plastics in the world, which is why vapor barriers are able to withstand years of moisture exposure without breaking down. Because regular plastic sheets were not made with foundation waterproofing in mind, they tend to be too thin to be effective against water vapor. Vapor barriers like WallSeal™ are 20-mil thick and designed to be durable and difficult to tear. The same cannot be said for regular plastic, which can be torn through and pierced with sharp objects. Another difference between the two is the different ways they interact with bacteria.

Regular plastic sheets have no protection against bacteria. After years of being in your basement, a regular plastic sheet can harbor so much bacteria that mold grows on the sheet. Mold may not be able to eat plastic, but it can eat the bacteria on the plastic with no problem. Vapor barriers like WallSeal™, on the other hand, have antimicrobial properties that protect them against bacteria and mold. So, although they look similar, you cannot use a plastic sheet in place of a real vapor barrier.