AS9120B, ISO 9001:2015, and FAA AC 0056B ACCREDITED

The Difference Between Air and Vapor Barriers

In high-performance structures with conditioned air, the walls between the interior of the building, aircraft, or other structure, alongside the outside environment, rely on two types of barriers to prevent a number of issues. Especially in aircraft that are high up in the atmosphere, the external and internal environments are more extreme, so barriers within the walls must create a reliable seal to prevent the internal environment from exposure to the external environment and vice versa. With concerns like loss of conditioned air, too much moisture, and other issues of air quality, air barriers and vapor barriers work together to keep the environment within walls stable.

While both air barriers and vapor barriers are extremely important components of safely sealed structures, they each function differently. The purpose of an air barrier is to mitigate air flow between a conditioned indoor space and an unconditioned outdoor space. Available in a myriad of materials from foam to concrete, glass, and so much more, all air frames should meet the same general requirements. First, they must be impermeable to air flow, meaning they prevent any exchange of air between the two environments between which they are situated. Second, they must be continuous over the entire structure to create a fully sealed indoor environment where air is trapped. Lastly, they must be durable in the sense that they do not wither nor fail under the conditions of construction or use.

There are two types of air barriers, interior and exterior, and the two are used in tandem as complementary designs. Interior barriers work to keep internal conditions inside by preventing the leakage of interior air and moist air into the wall cavity. This is important for when the internal environment is heated compared to a cooler external environment. Meanwhile, exterior air barriers prevent air from entering the internal environment and limit moisture when the internal environment is cooled compared to a warmer external environment. Ideally, the two should be used together to enhance their benefits in all conditions.

Meanwhile, a vapor barrier or vapor retarder is used to limit the movement of water vapor through a material. They are installed on the warmer side of the structure, meaning the vapor barrier will be on the outside in warm climates and on the inside in cold climates. Similar to air barriers, vapor barriers are available in a number of materials, including mechanically fastened sheet-material, adhesive membranes, and more.

Unlike an air barrier, a vapor barrier does not have to be continuous across the structure, as it is not a complete seal off from moisture. Instead, it allows limited vapor diffusion, so any inconsistencies in the barrier would only create an area where diffusion could occur at a faster rate. Understanding the functions of both air barriers and vapor barriers is important to your knowledge of your structure’s needs.

Together, air pressure and moisture control are crucial elements of a reliable structure. Air leaks and undesirable moisture levels can cause a great number of problems ranging from unwanted elements inside the structure like noise and fluctuating temperatures to complete structural failure. As such, there are a few key benefits to be reaped from installing an air barrier. First, make sure your wrap will successfully contain your internal air’s environment. This will prevent uncomfortable inside conditions and save costs on HVAC and insulation equipment. Second, your air barrier will lower utility bills. Additionally, air movement brings water vapor movement, so air barriers prevent moisture damage across critical areas of the structure’s walls. Lastly, the overall air quality of your structure will be improved and less susceptible to undesirable conditions of the external environment.

To begin procuring any materials and part types you require for your barrier-controlled structures, look no further than Fastener Orbit, a leading online distributor of high-caliber items for various applications and industries. Simply browse our website for any items you require and submit an RFQ form to receive an Instant Quote for your comparisons. For further questions, contact us at any time via phone or email; we are available 24/7x365! 


February 19, 2023
December 2, 2022

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