Coex Films: Construction and Application Possibilities in Detail
Last updated: 05 February 2026
Coex films are multilayer plastic films made from thermoplastic polymers such as polyethylene (PE) and polypropylene (PP). In addition, a core layer of EVOH (ethylene-vinyl alcohol copolymer) serves as an important barrier component for aseptic applications. In contrast to mono-films, modern coextruded high-barrier films usually consist of five to nine material layers. This complex structure is necessary to reliably combine the required mechanical properties with chemical barriers in the process. During a coextrusion process, several plastic layers are fused into a single composite film. Depending on the layer composition, different protective and functional properties result. Due to their functional nature, coextruded films are an established industrial standard in regulated sectors.
Types of Coex Films
Aseptic composite films can be divided into endless liners and pre-fabricated cleanroom bags. In addition to conventional packaging applications, these versions are suitable for the batch filling of highly active substances. Coextruded endless liners are classified within the closed FlecoLiner system for the contamination-free filling and handling of solids. In combination with the FlecoTec principle, these solutions enable a containment level of up to OEB 5, which is verified by corresponding validation documents from Rommelag FLEX. The same applies to customizable cleanroom bags, which can be used as primary and secondary packaging. Furthermore, high-barrier films protect sensitive contents such as food or pharmaceuticals from environmental influences.
Modern Manufacturing Technologies with High Quality Standards
In the production of multilayer composite films, the simultaneous processing of thermoplastic plastic granules takes place. Coextrusion represents the key technology within the manufacturing process. In this step, several extruders homogenize the plastic granules using a rotating screw. At the same time, depending on the polymer, the material liquefies into a viscous mass at temperatures between 180 °C and 250 °C. Subsequently, the multilayer plastic melt reaches slot-like dies upon leaving the extruder zone. This element is precisely configurable in terms of flow rate, temperature, and gap width, giving the film the desired material thickness. The flexible production process enables the manufacture of tailor-made packaging solutions based on individual customer needs. After extrusion, the film solidifies in a subsequent cooling process, which stabilizes the geometric profile of the material. To avoid particle contamination, film production takes place in a cleanroom environment that corresponds at least to ISO Class 7 (or higher, depending on specification) and is continuously monitored in accordance with GMP guidelines. Finally, the films undergo extensive testing procedures according to current standards to meet industry-specific quality and safety requirements.
The Versatile Fields of Application for Coex Films
For coex films, a wide range of applications results from the multifunctional structure. In the pharmaceutical industry and the biopharmaceutical sector, coextruded films form the basis for flexible primary packaging such as infusion bags or single-use systems. They thus complement the Rommelag portfolio where large-volume, flexible solutions outside of classic BFS applications (Blow-Fill-Seal / bottelpack) are required. Due to the high cleanroom quality, they are ideally suited for packaging pharmaceuticals, medical consumables, and surgical instruments. In the medical field, flexible films made of low-density polyethylene (PE-LD) with good sterilizability play a central role. Furthermore, composite films are suitable as tear-resistant security shipping bags as well as protective packaging for samples and oxygen-sensitive substances in chemical laboratories. In the food industry, the films also reliably protect against external influences and guarantee long shelf lives. Here, airtight packaging convinces through the use of LLDPE (linear low-density polyethylene) as a high-performance sealing layer in combination with integrated barrier layers that reliably protect sensitive goods from oxidation. Another area of application is the cosmetics industry, where multilayer films serve as hygienic packaging for personal care products such as shower gels, shampoos, or creams. In addition, antistatic films are used in explosive environments with flammable substances and combustible gases.
Material Properties of Coex Films
- Barrier effect: The dense molecular chains in the polymer layers shield the packaging contents from moisture, oxygen, carbon dioxide, and other influences. Furthermore, the film acts as a barrier layer and prevents the diffusion of gases, which ensures permanent quality preservation, especially for products with a modified atmosphere. Additionally, the barrier protection contributes to active ingredient stabilization, prevents aroma loss in food, and protects organic substances from oxidation.
- Mechanical stability: Through the combination of different polymer layers, composite films convince with a tear-resistant and puncture-resistant structure. Thus, the films withstand intensive loads and maintain their shape and integrity in demanding industrial applications. Depending on the area of application, functional properties such as elasticity, stiffness, or UV resistance can be enhanced by adding additives.
- Suitability for sealing: Coextruded films have a heat-sensitive sealing layer that fuses with other layers under the influence of heat and pressure. The sealable layer structure is primarily used for products whose packaging requires hermetic tightness. When opening the packaging, the contained additives in the form of release and anti-adhesive agents ensure residue-free detachment.
- Chemical resistance: Thanks to the resistant protective barrier, composite films prevent chemical interactions with the packaging contents. The polymer layers reliably protect against solvents, oils, substances containing alcohol, and weak acids. Here, polyethylene serves as the base material due to its inert properties and, in combination with polyamide or EVOH layers, creates a comprehensive barrier effect. If required, customized recipes with mixed additives enhance chemical resistance.
- Electrically dissipative: An effective solution to avoid electrostatic charging is electrically dissipative films. Electrical charges can flow away in a controlled manner and without spark formation via the dissipative layers. In this way, antistatic or conductive additives protect sensitive electronic components from uncontrolled discharges and functional damage.