Feuchtigkeitsempfindliche Produkte richtig verpacken – Aluminiumfolie, Blister, Laminate

Effective protection for moisture-sensitive products is not achieved by a single film rating; rather, it is achieved through a coordinated packaging system. The product condition, storage conditions, material selection, packaging design, and sealing must all be compatible with the intended shelf life. The WVTR of a film limits the water vapor ingress; however, in isolation, this does not indicate a specific shelf life or the tightness of the finished package. ^{[5] [7]}

Proper packaging of moisture-sensitive products means defining the protective objective before selecting the material. The most important factors are the tolerable product change, the initial moisture level, and the expected storage conditions. Moisture already contained in the product can condense when temperatures change, even without new water vapor entering the packaging from the outside. ^[2]

Product protection begins with product condition and storage conditions

For product protection, two different moisture loads must be considered separately: the slow entry of water vapor and the formation of condensation water. Water vapor can affect moisture-sensitive materials, even though no visible droplets are present. Depending on the product and load, sources such as deformation, corrosion, or mold can be favored, among others. Condensation water, on the other hand, is liquid water that forms when moist air cools down to its dew point on a sufficiently cold surface. ^{[1] [2]}

The distinction has direct consequences for the selection process. A vapor barrier limits the entry of additional moisture from the outside. However, it does not remove moisture that was already present in the product or in the headspace during packaging. If the temperature drops sufficiently, this initial moisture can condense within the package. A low WVTR value therefore does not answer the question of moisture-free packaging nor the question of a certain protection duration. ^{[2] [3]}

The protection objective must be determined before the material selection is made. Only the permissible moisture-related changes in product performance combine barrier requirements, storage conditions, and time into a reliable specification. Without a defined product limit, no numerical WVTR target value can be derived. The geometry of the final package is also important, because it influences the effective barrier area and the design of the closure. ^[5]

A viable packaging specification combines the following inputs:

• Acceptable product variation: It must be described what level of humidity or what quality change is still acceptable. Only this limit makes a concrete barrier requirement possible.
• Initial state: The humidity of the product and the conditions inside the packaging when sealing are relevant. An increased initial humidity not only affects subsequent vapor transport but also the risk of trapped moisture.
• Storage duration and operating environment: Temperature fluctuations, relative humidity and possible cooling periods determine the duration and intensity of the strain.
• Package geometry: Format, barrier area and closure design are requirements because material data alone do not describe the finished packaging.

If no information is provided regarding product tolerance, initial moisture content, or the temperature profile, the material selection remains tentative. Candidates can then be classified based on their data sheets, but their suitability for the intended storage conditions cannot be reliably determined.

Understanding WVTR and making material data comparable

WVTR stands for water vapor transmission rate. It describes the mass of water vapor that passes through a specific material surface within a given time period. In the case of packaging films, this usually occurs in g/(m²·day). In identical test conditions, a lower WVTR means less vapor transport. ^[3]

The figure is only meaningful in its context of testing. For a factual comparison, it must be documented with which testing method and at which temperature, relative humidity and material thickness the value was determined. Only these details create a common basis for comparison. If they are missing, a lower declared value does not justify a reliable ranking.

The demarcation with Permeability coefficients It is important: WVTR describes the measured transmission of a specific sample under specific conditions. The permeability coefficient, on the other hand, is a material-specific characteristic. If these two values are mixed together, film structures can be incorrectly classified based on seemingly similar numbers.

ASTM F1249 serves as the process standard for measuring WVTR on flexible barriers. ASTM E96/E96M-12 is an historical standard publication and does not constitute proof of current standard compliance. Even a computational adjustment to a different film thickness or a different partial vapor pressure gradient does not automatically create comparability. Therefore, for material selection, similar WVTR data with documented test conditions should be available for all candidates. ^{[3] [4] [6]}

Material selection and packaging design are decided jointly

A film with an appropriate WVTR value is only one component of moisture protection. The crucial factor is the shaped and sealed package. Surface and packaging geometry influence fabric transport, while folds, creases, transitions and the seal can create additional vulnerabilities. Therefore, data for flat film cannot be directly used to determine how well a specific packaging form protects the product.

In individual documented cases, the permeability of folded packages was higher than expected from data on flat film. Another case points to the possible influence of the seal on moisture ingress. No general error rate can be derived from this. However, the practical consequence remains clear: material data must not be extrapolated to the entire package without considering the design, seal, and processing. ^[7]

Hypothetical decision case: No ranking based on non-comparable data

For a moisture-sensitive product, two packaging candidates are available for selection. Candidate A has a lower WVTR than Candidate B. However, the values were measured under different temperature and humidity conditions. Additionally, it is not known with what initial humidity product and headspace are packaged.

A ranking based solely on the declared WVTR would not be reliable. The values do not have a common basis for comparison, and the unknown initial state leaves the risk of condensation open. Already contained moisture can condense at a temperature drop, without the need for water vapor to have previously entered from the outside. ^[2]

The selection process therefore follows: First, comparable WVTR data and the initial state of the product and its packaging are created. Subsequently, the remaining candidates are evaluated as formed, sealed packages, including folds, closures, and stresses from processing and transport. This specification separates the material rating from the protective effect actually required by the packaging system.

Quality control: Which test answers which question?

A material characteristic only describes the behavior of a defined sample under specified conditions. For packaging approval, additional evidence is required for the shaped, sealed package. Does it achieve the required moisture barrier as a unit? Will the sealing seam withstand mechanical stress? Are there local leakage paths at the closure? These questions relate to different types of defects and require separate proofs.

A reliable seam can be leaky. Conversely, a dense seal can allow too much water vapor to pass through surfaces, folds, or sealing areas despite intact sealing. The barrier clearance must therefore not solely be based on data from the source material. ^[7]

1. Translate the protection question into a verification question: First, it is determined whether the critical defect is excessive water vapor leakage across the entire package, a mechanically weak seam, or a localized leak. In this way, a favorable single test result is not mistakenly interpreted as approval for another type of defect.
2. Evaluate the overall barrier on the finished package: If acceptable moisture absorption, operating climate, and intended protection duration are relevant, the shaped and sealed packaging must be considered as a system. This view covers geometry, folds, and the proportion of the seal.
3. Treating tightness as a mechanical issue: In the case of seal packaging, the strength test shows whether the connection withstands the intended load. If it is insufficient, the root cause analysis focuses on the connection and processing. It does not replace a seal integrity test. ^[8]
4. Demonstrate tightness separately: A leak test appropriate to the packaging form and the expected defect pattern examines local paths of entry for moisture. Its suitability depends on the design and the question being asked. High seam integrity alone does not guarantee tightness. ^[8]
5. Addressing material change as a new process issue: A change in the packaging material or the source of the material can alter the processing window and thereby favor wrinkles or defective sealing seams. Therefore, a previous approval cannot be automatically transferred to the new material processing combination. ^[8]

Conclusion: The protective requirement determines the packaging

Material data enable a preliminary selection, but do not replace a complete basis for decision-making. If product limits, initial conditions, or relevant storage conditions are missing, a WVTR value cannot be used to derive a reliable suitability for the intended use.

The final assessment therefore concerns the finished package: Only the interplay of selected materials, design, closure and processing shows whether the specified protective effect can be evaluated in a verifiable manner under the specified conditions.