Meaning
Measurement of the passage of water vapor through a barrier material over a specific time and area under controlled temperature and humidity conditions defines barrier performance. Packaging engineers measure the moisture vapor transmission rate to evaluate the protective capability of plastic films and sheets. This value determines how effectively a container protects its dry contents from ambient humidity.
Testing Protocol
Standardized test procedures use either a gravimetric method or an instrumental sensor to detect moisture passage. When a laboratory evaluates a film, the moisture vapor transmission rate is calculated by sealing the material over a dish containing desiccant and exposing it to a humid atmosphere. The increase in weight over time corresponds to the amount of water that has penetrated the barrier.
Modern high throughput facilities use infrared or coulometric sensors to speed up this determination under precise climate control.
Material Selection
Design requirements for sensitive electronics or pharmaceuticals dictate strict barrier limits. Selecting a film with a very low moisture vapor transmission rate ensures that the packaged product stays dry throughout its intended distribution cycle. High density polyethylene offers moderate protection, while specialized coextruded films containing metalized layers yield much lower transmission rates.
This difference in barrier level directly affects the total material cost of the protective packaging.
Shelf Estimation
Storage life calculation depends on the transmission rate of the barrier under expected regional climates. If a developer uses a higher transmission rate material than specified, the internal humidity of the package rises too quickly and causes product spoilage. Mathematical modeling combines the transmission rate with the product’s sorption isotherm to predict the exact month of failure.
