Barrier resins for packaging applications are plastic films that protect the package contents from infiltration of gases, such as oxygen or water vapor, that may cause spoilage or degradation of the contents. Barrier resins also seal in the flavor or aroma of packaged foods or beverages. While plastics compete with glass and metal in barrier packaging, they have some advantages over these older materials. Among them: flexibility, light weight and relatively low cost.
The most common barrier resins used in packaging are polyvinylidene chloride (PVdC), ethylene vinyl alcohol (EVOH), PET, polychlorotetrafluoroethylene (PCTFE), nylon, and nitrile copolymers.
Most barrier resins are used in multilayer packaging structures, although some are used in monolayer structures. Typically, the outer layers of the multilayer packages are strong, transparent films made of such materials as polyesters or polypropylene, while the middle layers are made of the barrier resins. The layer that comes into contact with the packaged contents is often composed of low-density polyethylene.