Moisture Absorption Testing of Packaging Materials: Methods, Standards, and Applications

Moisture absorption testing evaluates how packaging materials take up and transmit water vapor under controlled temperature and humidity conditions, providing critical data for material selection, quality control, and shelf-life validation. This guide covers the standard test methods, sample types, measurable parameters, and internationally recognized standards such as ISO 62, ASTM D570, and ASTM E96 used by accredited third-party laboratories. Understanding these procedures helps manufacturers ensure that packaging maintains its barrier performance, dimensional stability, and protective function throughout the supply chain.

Technical Overview

Hygroscopicity, or moisture absorption, refers to the tendency of a packaging material to absorb and retain water molecules from the surrounding environment. Virtually all common packaging materials interact with ambient moisture to some degree: paper and paperboard absorb water readily through hydrogen bonding with cellulose fibers, nylon (PA) and EVOH polymers absorb water into their molecular structure, and even polyolefins such as PE and PP absorb trace amounts that can influence sealing and barrier behavior. Quantifying this behavior is essential because absorbed moisture alters mechanical strength, dimensional stability, printability, and barrier performance.

Moisture absorption testing is performed by exposing conditioned specimens to defined humidity atmospheres or immersion environments and measuring the resulting mass change gravimetrically. The tests are typically conducted in climate-controlled chambers at standardized atmospheres such as 23°C and 50% relative humidity (ISO 291, ASTM D618, GB/T 2918), or under accelerated tropical conditions of 38°C and 90% relative humidity for high-barrier evaluations. Results are expressed as a percentage mass gain and can be extended to derive parameters such as diffusion coefficients and equilibrium moisture content.

The consequences of excessive hygroscopicity in packaging are significant: weakened corrugated boxes that collapse under stacking loads, degraded water vapor barrier layers that shorten food shelf life, blistered or delaminated laminates, and corrosion of moisture-sensitive products such as electronics and pharmaceuticals. Moisture absorption testing therefore forms a core component of packaging validation programs, transport simulation studies, and shelf-life modeling across industries.

Testing Samples

Plastic Films, Sheets, and Laminates

Flexible packaging materials including monolayer films (PE, PP, PET, PA, PVC), multilayer laminates, metallized films, and high-barrier structures containing aluminum foil or EVOH. These samples are tested both for moisture absorption and for water vapor transmission rate to characterize total moisture management performance.

Paper and Paperboard Materials

Kraft paper, corrugated fiberboard, solid bleached and unbleached board, cartonboard, and molded pulp. Because cellulose-based materials are strongly hygroscopic, moisture content determination and humidity cycling are critical for evaluating compressive strength (BCT/ECT) retention during distribution.

Protective Foams and Cushioning Materials

Expanded polystyrene (EPS), expanded polyethylene (EPE), polyurethane foams, and air pillow films used for cushioning. Moisture uptake in these materials affects shock absorption properties and can contribute to condensation inside sealed packages.

Barrier, Bio-Based, and Specialty Materials

Moisture barrier bags for electronics, desiccant sachets and humidity indicator cards, biodegradable polymers such as PLA and cellulose-based films, adhesives, and coatings. Bio-based materials typically exhibit higher hygroscopicity than conventional plastics and require careful characterization for moisture-sensitive applications.

Testing Items

Moisture absorption test programs for packaging materials typically include the following measurable parameters:

• Moisture absorption rate (percentage mass gain after exposure to defined humidity conditions)
• Equilibrium moisture content (EMC) at various temperature and humidity setpoints
• Water absorption after immersion (23°C water immersion, long-term immersion, and boiling water immersion per ISO 62 and ASTM D570)
• Water vapor transmission rate (WVTR) and water vapor permeance of films and laminates
• Moisture content of paper and board by oven drying (ISO 287, ASTM D644)
• Dimensional stability and hygroexpansion after humidity conditioning
• Retention of mechanical properties (tensile strength, burst, compressive strength) after humid aging
• Diffusion coefficient and moisture sorption isotherm modeling for shelf-life prediction

Testing Methods

Gravimetric Water Absorption Method (ISO 62 / ASTM D570 / GB/T 1034)

This is the fundamental method for rigid and semi-rigid plastics. Specimens are dried to constant mass, cooled in a desiccator, and weighed to obtain the initial mass (m1). They are then either immersed in distilled water at 23°C for 24 hours, exposed to 50% relative humidity, or subjected to boiling water immersion for accelerated evaluation. After exposure, surface water is removed with a lint-free cloth and the specimens are reweighed (m2). Water absorption is calculated as (m2 − m1) / m1 × 100%, with thickness-dependent corrections applied where required by the standard.

Climatic Chamber Conditioning and Damp Heat Testing

Specimens or complete packages are placed in environmental chambers that maintain precise temperature and humidity conditions, for example 40°C/93% RH or 38°C/90% RH for tropical simulation. Steady-state damp heat testing is performed per IEC 60068-2-78, while cyclic damp heat testing per IEC 60068-2-30 evaluates resistance to condensation cycles that mimic day-night temperature swings inside shipping containers. Mass gain is recorded periodically until equilibrium is reached, and functional properties are assessed after exposure.

Water Vapor Transmission Rate Testing (ASTM E96 / ISO 2528 / ASTM F1249 / ISO 15106 / GB/T 1037)

WVTR testing complements absorption testing by quantifying how quickly moisture passes through a material. The gravimetric cup or dish method seals a desiccant or water reservoir behind the test film, and weight change is tracked over time. Modern instrumental methods use modulated infrared sensors (ASTM F1249), electrolytic detection (ISO 15106-3), or infrared sensor technology (ISO 15106-2) to deliver rapid, high-resolution results, particularly for high-barrier structures used in pharmaceutical and electronics packaging.

Oven-Drying Moisture Content Method (ISO 287 / ASTM D644)

For paper and paperboard, specimens are weighed, dried at 105°C ± 2°C to constant mass, and reweighed. The moisture content is calculated from the mass loss relative to the original or dry mass. This method establishes the as-received moisture content that directly governs the mechanical performance of corrugated and carton packaging.

Applications

Moisture absorption testing supports packaging development and compliance across a wide range of industries:

• Food and beverage packaging: validating barrier laminates for dry foods, snacks, powders, and moisture-sensitive formulations, and supporting shelf-life modeling
• Pharmaceutical packaging: qualifying blister foils, high-barrier laminates, and container closure systems against moisture ingress requirements, including stability studies under ICH-style climatic zones
• Electronics packaging: verifying moisture barrier bags, desiccant capacity, and dry-pack performance for moisture-sensitive devices prior to reflow soldering
• Transport and export packaging: assessing box strength retention under container rain conditions and tropical humidity during ocean freight
• Industrial and preservation packaging: evaluating vapor-phase corrosion inhibitor (VCI) papers, barrier wraps, and sealed protective systems for machinery and spare parts
• Material development: characterizing new bio-based films, recyclable mono-material structures, and paper-based barrier substitutes against conventional plastics

FAQ

What is the difference between moisture absorption testing and water vapor transmission testing?

Moisture absorption testing measures how much water a material takes up into its own structure when exposed to humidity or immersion, expressed as percentage mass gain. Water vapor transmission testing measures the rate at which moisture passes through a material from one side to the other, expressed as g/m² per day. Both properties together determine how a package protects its contents.

Which standards are most commonly applied?

ISO 62 and ASTM D570 (with the Chinese equivalent GB/T 1034) govern plastic water absorption; ISO 287 and ASTM D644 cover paper and board moisture content; ASTM E96, ISO 2528, ISO 15106, ASTM F1249, and GB/T 1037 cover water vapor transmission; and IEC 60068-2-78 and IEC 60068-2-30 govern damp heat environmental testing of packages.

How long does a typical moisture absorption test take?

Immersion tests such as the 24-hour water absorption method can be completed in one to two days. Humidity conditioning to equilibrium may require several days to several weeks depending on material thickness and diffusivity, while WVTR instrumental methods typically deliver results within hours to a few days.

What sample size and preparation are required?

Requirements vary by standard, but typical specimens are discs or rectangles of 50 mm to 100 mm diameter with defined thickness, cut cleanly without cracks or edge damage. Specimens are normally pre-conditioned at 23°C and 50% RH, and for absorption testing are dried to constant mass before the initial weighing.

Why should testing be performed by an accredited third-party laboratory?

Accredited laboratories maintain calibrated environmental chambers, precision balances with traceability, validated test protocols, and experienced personnel, ensuring results are reproducible, internationally accepted, and suitable for regulatory submissions, supplier qualification, and customer audits.