Hochbarrierefolien: Aufbau und Materialauswahl – Aluminiumfolie, Blister, Laminate

The choice of a high barrier film is not based on a universally „best“ material class, but on the specific protection requirement: Should oxygen be kept away, moisture absorption or loss be limited, and light be shielded? Only when these protection requirements are determined in conjunction with storage duration, climate, transparency requirements, and mechanical load, can a suitable structure be selected.

The complete combination is always crucial. Aluminium, metallized films and EVOH can each be part of more effective multi-layer laminates, but they fulfill their functions in different ways and under different conditions. Therefore, a good rating for a single layer is not yet an indication of the later packaging performance.

How high-barrier films are constructed

High barrier films are usually multi-layer laminates: Several layers are combined because a single layer is rarely intended to fulfill both barrier properties, mechanical stability, sealability, and the desired appearance at the same time. For example, one layer repels gases, water vapor, or light, another protects the composite from strain, and the inner layer enables sealing of the packaging.

A schematic structure could be, for example PET/Aluminium/PE PET can stabilize the outer layer, while the independent aluminum foil provides a barrier against oxygen, water vapor, and light. PE can serve as a barrier against these elements while also acting as a seal layer. Adhesive layers are usually placed between the layers. This structure is a visual example, not a universal specification. In this structure, the aluminum layer combines the functions of gas, moisture, and light protection. ^[1]

The method of connection is also part of the technical specifications. In the case of laminated films, existing webs are joined; in the case of coextruded films, several polymer layers are created together. The criterion for preselection is less the method than the question of whether the finished composite retains the required protective effect under its actual operating conditions.

Special attention should be paid to integrity: A high material barrier does not automatically protect against weaknesses in the finished packaging material. Pinholes, i.e., the smallest imperfections, and creasing can facilitate penetration, especially in metallic barrier layers. Therefore, the strain caused by forming, assembling, filling, and transporting must be taken into account when evaluating the entire structure. ^[3]

Aluminium, metallized films and EVOH compared

The three concepts are not mere variants of the same layer. They differ in their structure, optical effect and the conditions under which they are suitable for use. The crucial question therefore is not which material is fundamentally better; rather, which composite material provides the required combination of oxygen, water vapor and light protection?

Aluminium foil: independent, light-proof barrier layer

In aluminum-based laminates, a genuine aluminum foil is included as a separate layer within the laminate. It forms a barrier against oxygen, water vapor, and light. This makes it a possible construction concept when the protective coating covers all three influences and transparency is not a requirement. ^[1]

This strength does not exempt the consideration of the finished packaging material. If the aluminum layer is severely bent or damaged during processing, imperfections can reduce the practical barrier. The selection must therefore take into account not only the nominal layer thickness but also the expected load on the composite.

Metallized films: vaporized metallization instead of aluminum foil

Metallized films are not to be confused with aluminum foil. In the case of metallized PET or BOPP, a very thin aluminum layer is vaporized onto a plastic film; this carrier film can then be bonded with additional layers, such as PE, to form a laminate. The metallization improves protection against oxygen, water vapor, and light; however, its actual barrier effectiveness depends on the respective quality and the complete structure. ^[2]

Metallic appearance is therefore not a sufficient selection criterion. Special high barrier qualities can approximate those of aluminum compounds, but this does not imply general equivalence or a fixed ranking. If an aluminum foil is to be replaced, the intended application requires comparable data regarding the finished composite and its condition after relevant processing. ^[3]

EVOH: transparent oxygen barrier with humidity-dependent properties

EVOH, an ethylene-vinyl alcohol copolymer, is incorporated as a functional polymer layer in co-extruded or laminated multilayer films. It can provide a high oxygen barrier and is therefore fundamentally suitable for transparent packaging concepts. However, EVOH does not replace a light-impermeable structure.

Its main selection limit is moisture. If the EVOH layer absorbs water, its oxygen barrier can weaken. Therefore, it is usually positioned between more moisture-resistant layers; polyolefins can take on the moisture barrier during construction, while EVOH provides the gas barrier. The layer position and adjacent materials are therefore not details, but determine whether a transparent solution remains a viable candidate under humid conditions at all. ^{[4] [7]}

Which barrier data are truly comparable

Data sheets are only then a reliable source of information for decision-making when they answer the same question. To do this, the oxygen and water vapor barriers must be read separately. OTR describes the oxygen permeability, which WVTR water vapor permeability. A good OTR value alone does not tell us anything about how effective a build is against moisture – and vice versa.

Values can only be compared with their test conditions. Temperature and relative humidity are essential, as they influence the permeability of plastic packaging. Especially with EVOH, measurements under dry conditions can only insufficiently represent a humid real environment. Higher storage temperatures can also increase the gas and water vapor permeability. ^{[4] [6]}

For a professionally accurate comparison of offers, at least the following information should be available:

• Proven construction: Material layers, layer sequence, and, where available, the associated construction definition. A characteristic value for an isolated layer does not replace the indication of the assembly.
• OTR and WVTR: Both values separately, each with temperature, relative humidity and measurement method or data sheet context.
• State of strain: Whether the data apply to the unprocessed film, the further processed composite or a finished shaped packaging.
• Mission profile: Actual storage and transport conditions, contact with wet fill materials, and the desired protection duration.

If one of these details is missing, no reliable superiority can be derived from a lower value. An OTR under varying relative humidity answers a different question when used in a humid environment than the value of the final composite. Similarly, a value for a flat-pressed film can reveal how folds, seal areas, or the intended processing will affect it. The appropriate consequence is not to replace the missing value with a material assumption. Instead, the selection remains limited to those structures for which comparable information is available or can be specifically requested.

The same logic applies to light protection: The absence of transparency or the absence of an impermeable layer does not yet result in a specifically quantifiable protective effect. For this to be the case, appropriate transmission data for the entire composite would be required. Without these data, a transparent structure cannot be categorically ruled out nor classified as sufficiently light-protective.

A single laboratory result does not constitute a guarantee of shelf life. The packaging can only be evaluated conclusively in conjunction with the specific product and under the intended conditions. Therefore, for food products, the selection should be based on the expected loss of quality, for example due to oxidation or moisture absorption or loss. ^[5]

From the need for protection to the justified pre-selection

A reliable pre-selection occurs in a clear order. This prevents a material from being preferred because of its name, appearance, or isolated peak value, even though another requirement excludes it.

1. Name quality changes. First, it is determined what the packaging is intended to prevent: oxidation, moisture exchange, light damage, or a combination thereof. Based on this, the relevant barrier types are determined.
2. Determine the protection duration and operating environment. Storage duration, temperature, relative humidity and transport stress indicate the conditions under which the barrier must function. Without this profile, OTR and WVTR data remain only partially meaningful.
3. Use optical requirements as a disqualifying criterion. If the content must remain visible, translucent structures are not a direct solution. If a specific light protection effect is required, it must be demonstrated for the complete structure using appropriate transmission data.
4. Filter material concepts based on their layer function. Aluminum foil remains a possible construction concept for combined light, moisture, and oxygen protection. Metallized foils remain in the running only with proof of construction. EVOH is relevant for transparent oxygen barriers, but requires appropriate protection from the surrounding layers for moisture.
5. Have the complete association verified. Data are compared under appropriate climatic conditions and based on the expected processing method. Only then can a suitability assessment be carried out using the product and the planned packaging.

Hypothetical decision case: Transparent food packaging requires oxygen protection; at the same time, a moist environment is to be expected. Transparency excludes a light-impermeable aluminum layer as an immediate solution. EVOH remains a possible candidate as a transparent oxygen barrier, however, only if the EVOH layer is sufficiently protected from moisture through the multi-layer structure and the bonding performance is confirmed under the relevant conditions. ^{[4] [7]}

If a defined light protection requirement is added, the decision-making process becomes more complex. The transparent design can meet the optical requirement, but its light protection effect is not determined. The consequence is not an automatic rejection of transparent concepts, but a clear data gap: Information is required for the preliminary selection regarding the total transmittance of the entire assembly under the relevant load conditions. If this information is missing, the design remains unrated for the combined protective application, even if its oxygen barrier appears plausible.

Charge related to the usable packaging

Economic efficiency only begins after technical pre-selection. A lower price per film quantity is not a viable advantage if the offered solution does not meet the protection requirement or additional process steps are required. Therefore, only technically suitable structures that have been evaluated under comparable conditions should be compared.

The appropriate size of the packaging is the usable, specification-compliant packaging – not just the purchased mass or area of film. The comparison includes material consumption, proven waste, the impact of processing on the barrier, and actually required additional measures. These may include, for example, measures to reduce oxygen during packaging or the use of oxygen absorbers, provided that they are necessary for the specific solution. ^[5]

Without real process data, one cannot derive either price advantages or savings from this. However, the method prevents a typical error: A solution is not economically advantageous because it appears cheaper when purchased, but because it achieves the required protective function as a usable packaging with the effort actually required.

Conclusion: Requirements lead to the appropriate structure

High barrier films are not selected based on the material name, but on the interaction between protective requirements, layer structure and application conditions. Aluminum, metallized films and EVOH are different tools for different protective profiles. A documented requirement profile with separate requirements for oxygen, moisture and light creates the basis for comparable offers. The final suitability is only demonstrated when the complete assembly is completed under the intended conditions.