It refers to the defined package specimen, rather than automatically to one square metre of film. Film OTR may use cm³/(m²·day), while package OTR may use cm³/(package·day). Identify whether the specimen is a complete card, one cavity or another prepared package.
For moisture, distinguish a measured mass gain from a rate. A per-cavity daily rate also needs a stated time interval and normalisation basis; it is not interchangeable with an unqualified package weight gain.
Can a card result simply be divided by the number of cavities?
Division produces an average per nominal cavity only if the numerator and specimen boundary genuinely cover those cavities on the stated basis. It does not demonstrate that every cavity has that same transmission. Keep the card result and any normalisation visibly separate.
Identify which cavities and seals belong to the specimen and how it was mounted. Package and film fixtures can expose different boundaries, so the fixture and specimen preparation remain part of the result.
Fields needed to interpret a whole-package result
Report field
Reason to retain it
Package boundary
Defines card, cavity or other measured specimen.
Permeant and unit
Distinguishes oxygen volume, moisture mass and time basis.
Conditions and method
Identifies temperature, humidity and gas conditions.
Reported vs normalised value
Separates actual measurement from a per-cavity calculation.
Flat-film calculations and finished-pack measurements
A simple area calculation is not a measurement of the finished blister. Flat film and a formed, sealed pack have different geometry and processing histories. Keep local thickness distribution and the complete prepared specimen within the package-evaluation scope.
Package transmission quantifies transfer across the tested boundary. Locating a defect and establishing product storage life require separate assessments.