Multi-layer film is the broader product category created by coextrusion. While a monolayer film relies on a single resin or resin blend to deliver every property a package needs at once, including strength, sealability, barrier, printability, and machinability, multi-layer film spreads those jobs across separate layers, each one optimized for its own task. A film might have anywhere from three layers up to eleven or more on the most advanced equipment, with total structure thickness still landing in a normal packaging gauge range.
This layered approach lets converters hit performance targets that would be difficult or prohibitively expensive with a single resin. For example, a structure might pair an outer skin layer formulated for good printability and slip, a structural core of LLDPE for toughness, and a sealant layer of LDPE or a specialty sealant resin for consistent, reliable seals, all in one film rather than requiring a separate laminated film and adhesive.
Multi-layer film has largely replaced laminated structures (separate films glued together after the fact) for many packaging applications because it accomplishes a similar layered performance profile in a single extrusion step, which is generally faster and less costly than lamination, though true laminations and coatings still have a place for certain barrier or print requirements multi-layer coextrusion can't match.
Glossary
Multi-Layer Film
Film made of two or more distinct resin layers bonded together during extrusion, each layer engineered to deliver a specific performance property.
Example
A heavy-duty shipping sack made as a three-layer coextruded film can combine an abrasion-resistant outer layer, a tough LLDPE core, and a sealant inner layer, all without needing a separate lamination step.
Nuance
Multi-layer film and laminated film are sometimes used interchangeably in casual conversation, but they're produced very differently. Multi-layer (coextruded) film is formed as one continuous extrusion event with all layers molten and bonding simultaneously, while a laminate is made by gluing or extrusion-coating separately produced films together after the fact. The distinction matters for cost, recyclability, and achievable structures.