Vapor Barrier vs Vapor Retarder

The main goal of installing a vapor barrier liner is to control moisture diffusion. When ground moisture enters the structure through the floor slabs, it can cause the wood to rot and trigger the growth of mildew and mold. Moisture can also build up in the walls and the attic, causing poor air quality.

A vapor barrier is a type of vapor retarder. It is the permeability level that makes it a vapor barrier.

There are 3 classes of permeability for vapor retarders.

Vapor barriers are classified under Class I and Class II.

A Class I Vapor retarder has a perm of 0.1 or less, meaning it’s impermeable. This is usually a non-perforated aluminum foil sandwiched between 2 sheets of 6 mil polyethylene. It blocks the moisture entirely.

A Class II Vapor retarder has a perm of 0.1 to 1.0 perms. This is what the crawl space and radiant barriers fall under and it’s considered semi-impermeable.

A Class III Vapor Retarder has a perm of 1.0 to 10 perms. Class III vapor retarders are generally latex or enamel paints and they are permeable.

Choosing the right Vapor Retarder

Choosing the right “Vapor Retarder” is important when it comes to the matters of your home or building. That’s why our specialists are thoroughly educated on the liners we sell to advise the best product for your application. The specs are available on our site so you can see for yourself how the product measures up.