Barrier film is built to control transmission rates of gases like oxygen and water vapor through the package wall, which is critical for food, pharmaceutical, and many industrial products that degrade when exposed to air or moisture. Performance is typically described using oxygen transmission rate (OTR) and water vapor transmission rate (WVTR), both measured under standardized test conditions and expressed as the amount of gas that passes through a given area of film over a given time.
No single common polyolefin offers strong barrier against both oxygen and moisture at once, so barrier film is almost always a multi-layer coextruded structure. Polyethylene resins like LLDPE and LDPE provide excellent moisture barrier on their own but are quite permeable to oxygen, while specialty resins like EVOH or polyamide (nylon) provide outstanding oxygen barrier but are themselves moisture sensitive and need to be protected by polyolefin layers on either side. Combining these resins into one coextruded structure, often with tie layers to bond them, lets a single film deliver both types of barrier at once.
The level of barrier required is entirely dictated by the product being packaged and its required shelf life; a fresh-cut produce bag needs very different gas transmission characteristics than a shelf-stable cheese package or a barrier bag protecting a moisture-sensitive industrial component, so barrier film specifications are always built around the specific application.
Glossary
Barrier Film
Film engineered to slow the passage of oxygen, moisture, or other gases, protecting the freshness, shelf life, or quality of what's inside the package.
Example
A shelf-stable snack food pouch that needs to stay crisp for months on a retail shelf will typically rely on an EVOH-based barrier layer sandwiched within a coextruded polyethylene structure to keep oxygen out and prevent the product from going stale.
Nuance
Customers sometimes ask for a film that is simply a good barrier without specifying against what, but oxygen barrier and moisture barrier are different properties that are often in tension with each other in resin selection. A film optimized to block oxygen, like one built around EVOH, is not automatically a strong moisture barrier, and vice versa, so it's important to clarify which gas or vapor actually threatens the packaged product's shelf life.