EVOH (ethylene-vinyl alcohol) is a type of plastic prized for its exceptional ability to block oxygen and other gases from passing through it. You’ll find it most often as a thin layer sandwiched inside food packaging, where it keeps products fresh far longer than ordinary plastic can. It also shows up in fuel tanks, floor heating systems, and even medical procedures where doctors need to seal off blood vessels.
How EVOH Is Made
EVOH is a copolymer, meaning it’s built from two different molecular building blocks: ethylene and vinyl alcohol. The catch is that vinyl alcohol is chemically unstable on its own and can’t be isolated, so manufacturers use a two-step workaround. First, they combine ethylene with vinyl acetate to create a stable intermediate material. Then they chemically swap out the acetate portions using methanol, converting the result into EVOH.
The ratio of ethylene to vinyl alcohol in the final product matters a lot. Less ethylene (around 32%) produces a better gas barrier. More ethylene (around 38% or higher) makes the material easier to process and more resistant to moisture, but lets more oxygen through. Manufacturers choose a specific ratio depending on what the packaging needs to do.
Why It Blocks Oxygen So Well
The vinyl alcohol segments of the polymer chain carry hydroxyl groups, small chemical features that form tight bonds with each other both within and between polymer chains. These bonds create a dense molecular network that gases struggle to penetrate. In multilayer packaging sheets, EVOH with 32% ethylene content allowed less than 1 cubic centimeter of oxygen per square meter per day to pass through. Bump the ethylene content up to 38%, and that number nearly doubles to 1.7. For context, standard polyethylene lets through hundreds of times more oxygen than either version.
This barrier performance is what makes EVOH the go-to material when shelf life matters. Ready-to-eat meals packaged with high-barrier EVOH-based pouches can last 3 to 5 years at room temperature.
The Moisture Problem and How It’s Solved
The same hydroxyl groups that make EVOH such a powerful oxygen barrier also attract water. When the material absorbs moisture, its gas-blocking ability drops significantly. This is why you’ll almost never find EVOH used as a standalone film.
Instead, manufacturers co-extrude it as the center layer in a multilayer sandwich. A typical structure places EVOH between outer layers of polyethylene or polypropylene. The outer layers serve double duty: they shield the EVOH from humidity while also providing a surface that can be heat-sealed and printed on. This combination gives you a packaging film with the moisture resistance of polyethylene and the oxygen barrier of EVOH, getting the best of both materials.
Where You’ll Find EVOH in Food Packaging
EVOH is everywhere in the food industry, though you’d rarely know it by looking at a package. It typically makes up only 3 to 5 percent of a multilayer film’s total thickness. Common applications include vacuum-sealed deli meats, cheese packaging, ketchup bottles, juice cartons, and thermoformed trays for ready meals. Any product that degrades when exposed to oxygen, which includes most foods, benefits from an EVOH layer.
The FDA regulates EVOH for food contact under 21 CFR 177.1360. The rules set strict limits on how much material can leach out of the film into food. For example, when tested with water at room temperature for 48 hours, the total extractable material must stay below 0.0047 milligrams per square centimeter of surface. These thresholds vary depending on the specific EVOH formulation and the temperature conditions it will face, but the material has a long safety track record in food applications.
Medical Uses: Sealing Off Blood Vessels
Outside of packaging, EVOH has found a surprising second career in medicine. Dissolved in a specialized solvent and mixed with a metallic powder that makes it visible on X-rays, EVOH forms the basis of liquid embolic agents, products that doctors inject through catheters to intentionally block blood vessels. The two best-known brands are Onyx and Squid.
When the liquid reaches a blood vessel, the solvent diffuses away and the EVOH solidifies from the outside in. This “magma-like” hardening pattern lets the material flow deep into small vessels before setting, giving doctors precise control over where the blockage forms. Originally developed in the 1990s to treat abnormal blood vessel clusters in the brain, these agents are now also used for stopping acute bleeding in other parts of the body, sealing leaks in vascular grafts, and cutting off blood supply to certain tumors.
Other Industrial Applications
EVOH’s barrier properties extend beyond oxygen. The material also resists the passage of fuels and organic solvents, which is why it’s used as a layer in automotive fuel tanks and fuel lines to meet emissions regulations. In construction, EVOH-lined pipes are used in radiant floor heating systems to prevent oxygen from entering the water loop, which would otherwise cause corrosion in metal components. Agricultural films, pharmaceutical blister packs, and cosmetics packaging round out its industrial resume.
The material processes at relatively high temperatures, with a melting point typically between 173 and 183°C depending on the ethylene content. Lower ethylene grades melt at higher temperatures but deliver better barrier performance, a tradeoff that engineers balance based on the specific manufacturing process and end-use requirements.