EVOH (Ethylene Vinyl Alcohol)

EVOH is a copolymer of ethylene and vinyl alcohol, and its hydroxyl groups give it an extremely tight, ordered molecular structure that is very difficult for oxygen molecules to pass through. Different grades are available with varying ethylene content, generally somewhere between 27 and 48 mole percent; lower ethylene content gives even better oxygen barrier but reduces moisture resistance and flexibility, while higher ethylene content trades some barrier performance for easier processing and better performance in humid conditions.

Because EVOH itself is sensitive to moisture (its oxygen barrier performance degrades when the resin absorbs water) and does not bond well to polyolefins, it is virtually never used alone. Instead, it's sandwiched as a thin internal layer, often just a few percent of total film thickness, within a coextruded structure where polyethylene or polypropylene layers on either side protect it from moisture and tie layers bond it to those surrounding layers.

EVOH shows up wherever a packaged product needs serious protection from oxygen exposure over an extended shelf life, including processed meats, cheese, certain sauces and condiments, and various industrial products sensitive to oxidation, making it one of the most important specialty resins in modern multi-layer barrier packaging.

A cured meat package designed for a 60-day refrigerated shelf life will typically rely on a thin EVOH layer at the core of a coextruded structure to keep oxygen transmission low enough to prevent spoilage and discoloration over that time.

It's a common misconception that more EVOH automatically means more barrier protection, but EVOH's barrier performance is highly sensitive to humidity and ethylene content, so simply adding a thicker EVOH layer isn't always the right lever. Protecting the EVOH layer from moisture with adequately thick polyolefin skin layers often matters as much as the EVOH layer's thickness itself.