Water Vapor Permeability Testing of Packaging by the Infrared Detection Method

Water vapor permeability testing by the infrared detection method is a high-sensitivity analytical technique used to determine the water vapor transmission rate (WVTR) of packaging films, laminates, and barrier materials. Governed by internationally recognized standards such as ASTM F1249, ISO 15106-2, and GB/T 26253, this method delivers rapid, precise, and reproducible results that are essential for quality control, shelf-life validation, and barrier material development across the food, pharmaceutical, and electronics industries.

Technical Overview

The water vapor transmission rate (WVTR), also known as water vapor permeability, is one of the most critical performance parameters for flexible packaging materials. Moisture ingress through packaging films can cause product degradation, loss of crispness in foods, hydrolysis of pharmaceuticals, corrosion of electronic components, and shortened shelf life. The infrared detection method has become the preferred laboratory technique for quantifying WVTR because it offers significantly higher sensitivity and shorter test cycles than traditional gravimetric (cup method) testing.

In this method, the specimen is clamped as a sealed barrier between two chambers of a permeation cell. One side of the specimen is exposed to a controlled atmosphere of high relative humidity, while the other side is continuously swept by a stream of dry nitrogen carrier gas. Water vapor that permeates through the specimen is entrained in the carrier gas and transported to an infrared sensor. Because water vapor absorbs infrared radiation at characteristic wavelengths, the sensor quantifies the concentration of transmitted water vapor with exceptional precision. Once the system reaches steady-state equilibrium, the water vapor transmission rate is calculated automatically and expressed in units of g/m²·24 h.

Modern instruments typically employ modulated infrared sensor technology, which enhances signal stability, minimizes drift, and extends the lower detection limit down to approximately 0.001 g/m²·24 h. This makes the technique particularly suitable for evaluating high-barrier structures such as aluminum foil laminates, metallized films, transparent oxide-coated films (AlOx, SiOx), and multilayer coextrusions containing EVOH or PVDC barrier layers.

Testing Samples

Monolayer Plastic Films and Sheets

Common monolayer materials submitted for infrared WVTR testing include polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyamide (PA), polylactic acid (PLA), polyvinylidene chloride (PVDC), and ethylene-vinyl alcohol copolymer (EVOH) films with thicknesses typically below 0.5 mm. Specimens must be flat, free from wrinkles, pinholes, and surface contamination, and should be conditioned in a standard laboratory atmosphere before testing.

Multilayer Laminates and Composite Structures

Flexible packaging laminates combining substrates such as PET/AL/PE, PET/met-PET/PE, BOPP/VMPET/CPP, and paper-aluminum-plastic composites are routinely evaluated. The infrared method is well suited to these structures because it accurately resolves the very low transmission rates achieved by foil and metallized barrier layers.

High-Barrier Functional Films

Vacuum-deposited films with aluminum oxide (AlOx) or silicon oxide (SiOx) coatings, transparent high-barrier films for OLED and photovoltaic encapsulation, and medical-grade Tyvek-type materials can be characterized thanks to the method's ultra-low detection limit.

Finished Packages and Containers

Beyond flat films, extended test cells and package fixtures allow the assessment of complete packages, including sachets, pouches, blister cavities, and bottles, providing insight into real-world package performance that includes the influence of seals, closures, and material transitions.

Testing Items

The core measurand of this test is the water vapor transmission rate (WVTR) of the specimen, expressed in g/m²·24 h, under specified temperature and humidity conditions. Typical reported items include:

• Water vapor transmission rate (WVTR) in g/m²·24 h
• Water vapor permeance in g/m²·24 h under dual atmospheric conditions
• Water vapor permeability coefficient in g·cm/(cm²·s·Pa) for homogeneous materials, where thickness is known
• Steady-state permeation curves and equilibration time data
• Comparative barrier ranking of candidate packaging structures

Testing Methods

Testing is performed in accordance with internationally recognized standards, most commonly:

• ASTM F1249 — Standard Test Method for Water Vapor Transmission Rate Through Plastic Film and Sheeting Using a Modulated Infrared Sensor
• ISO 15106-2 — Plastics: Film and sheeting; Determination of water vapour transmission rate; Part 2: Infrared detection sensor method
• GB/T 26253 — Determination of water vapour transmission rate for plastic film and sheeting by the infrared sensor method
• JIS K 7129-2 — Determination of water vapour transmission rate of plastic film and sheeting by infrared sensor detection

The general test procedure is as follows:

• Specimens are cut to the required dimensions and conditioned in a controlled environment, typically 23 ± 2 °C and 50 ± 5% relative humidity, to ensure representative results.
• The specimen is mounted and hermetically sealed in the permeation cell, isolating the humid chamber from the dry carrier gas chamber.
• The system is calibrated using certified reference films traceable to national metrology institutes to guarantee measurement accuracy.
• Test conditions are set — the most common being 38 °C with 90% RH (tropical condition) or 23 °C with 85% RH; conditions such as 40 °C/90% RH and 37 °C/90% RH are also frequently specified for accelerated studies.
• Dry nitrogen flows through the low-humidity side at a controlled rate, carrying permeated water vapor to the infrared sensor for continuous concentration measurement.
• When the transmitted vapor signal reaches steady state, the instrument calculates WVTR automatically and reports the final value, typically as the average of multiple specimens.

Compared with the gravimetric cup method described in ASTM E96 and ISO 2528, the infrared method offers faster equilibration, higher sensitivity for low-permeation materials, full automation, and reduced dependence on operator weighing technique. It is therefore the method of choice whenever accurate quantification of high-barrier packaging is required.

Applications

Infrared WVTR testing supports decision-making at every stage of the packaging lifecycle, from material selection to finished-product release:

• Food packaging: shelf-life modeling for snacks, bakery products, powdered beverages, coffee, dehydrated foods, and seasonings where moisture control directly governs crispness, caking, and microbial stability.
• Pharmaceutical packaging: qualification of blister films, sachets, and laminate pouches for effervescent tablets, hygroscopic powders, and moisture-sensitive solid dosage forms, supporting stability studies and regulatory submissions.
• Medical device packaging: verification of moisture barrier performance for sterile barrier systems and diagnostic reagent packaging.
• Electronics and optoelectronics: evaluation of moisture barrier bags, desiccant packaging, and transparent encapsulation films for displays, OLED devices, and photovoltaic modules.
• Research and development: comparison of barrier resin formulations, coating uniformity studies, and accelerated aging programs for new packaging structures.
• Quality control and supplier verification: incoming material inspection, batch release testing, and periodic verification performed by accredited third-party laboratories.

FAQ

What is the typical detection range of the infrared method?

Modern modulated infrared sensor instruments typically cover a range from approximately 0.001 g/m²·24 h up to several hundred g/m²·24 h, allowing both ultra-high-barrier foil laminates and relatively permeable monolayer films to be measured on the same platform.

How does the infrared method differ from the gravimetric cup method?

The cup method determines WVTR by weighing water gained or lost through a specimen over time, which is simple but slow and limited in sensitivity. The infrared method continuously quantifies permeated water vapor with a sensor, delivering much lower detection limits, shorter test times, higher repeatability, and full automation, making it superior for high-barrier materials.

Which test conditions are most commonly specified?

The most widely used condition is 38 °C with 90% relative humidity, reflecting tropical storage environments. Other common conditions include 23 °C/85% RH for ambient evaluation and 40 °C/90% RH or 37 °C/90% RH for accelerated aging and pharmaceutical stability studies.

How long does a single test take?

Test duration depends on the barrier level of the specimen. Medium-barrier films may reach steady state within a few hours, while ultra-high-barrier structures such as foil laminates may require 24 to 96 hours or longer. Instruments with automatic equilibrium detection end tests as soon as steady state is confirmed.

How should specimens be prepared for reliable results?

Specimens should be flat, defect-free, and representative of production material. They must be conditioned in a standard atmosphere before testing, sealed without leaks in the test cell, and tested in replicate — typically a minimum of three specimens — to account for material variability.

Can finished packages be tested instead of flat films?

Yes. With appropriate package fixtures and extended test cells, complete pouches, sachets, blister cavities, and bottles can be evaluated, capturing the combined barrier contribution of the material, seals, and closures under realistic conditions.