Oxygen Transmission Rate (OTR) is: under specified temperature and humidity, the volume of oxygen that passes through one square metre of packaging material per day, commonly expressed in cm³/(m²·24h). The lower the value, the stronger the material's oxygen-barrier capability.
Analogy: think of the packaging film as a "wall" and oxygen as an intruder trying to squeeze through it. OTR is the total amount of oxygen that gets through each day. The denser the wall (high-barrier material), the less gets through, and the slower the contents degrade.
Definitions in the standards
ASTM D3985-17 (Standard Test Method for Oxygen Gas Transmission Rate Through Plastic Film and Sheeting Using a Coulometric Sensor), clause 3.1.3, defines OTR as "the quantity of oxygen gas passing through a unit area of the parallel surfaces of a plastic film per unit time under the conditions of test" — SI unit mol/(m²·s), with cm³/(m²·24h) at one atmosphere pressure difference as the commonly used unit. The corresponding international method standard is ISO 15105-2 (equal-pressure method).
Units and typical ranges
High-barrier materials (aluminium-foil laminates, EVOH co-extruded films) can reach OTR values below 1 cm³/(m²·24h); medium-barrier polyamide (PA) films typically fall in the tens; ordinary single-layer PE or PP films can reach several thousands. Fatty foods, infant formula and oxygen-sensitive pharmaceuticals generally require high-barrier packaging, otherwise rancidity, nutrient loss and reduced drug potency occur.
Test method: the coulometric method
The specimen divides the test cell into two halves: oxygen flows on one side, while nitrogen carrier gas sweeps the transmitted oxygen molecules into a coulometric sensor on the other. Oxygen reacts at the sensor electrodes and produces a current proportional to the oxygen transmission, from which OTR is calculated directly. Relevant standards: ASTM D3985 (USA) 19789 (China), ISO 15105-2 (international). Its high sensitivity makes it the mainstream method for high-barrier materials.
Relation to WVTR and GTR
All three belong to the packaging-barrier family: WVTR measures water-vapour transmission, GTR measures various gases by the differential-pressure method, and OTR measures oxygen specifically. Most pharmaceutical and food packaging standards specify two or more of them, so QC laboratories normally need the corresponding instruments.
References
- ASTM D3985-17, Standard Test Method for Oxygen Gas Transmission Rate Through Plastic Film and Sheeting Using a Coulometric Sensor (ASTM International);
- ISO 15105-2, Plastics — Film and sheeting — Determination of gas-transmission rate — Part 2: Equal-pressure method (International Organization for Standardization).
- These are the primary authoritative sources for the definitions and test methods in this article.
