Understanding Oxygen Transmission Rate (OTR)

The Oxygen Transmission Rate (OTR) represents a core metric in packaging science. It quantifies the steady-state rate at which oxygen gas moves through a specific area of a barrier film over a defined period, all measured under controlled conditions of time, temperature, and relative humidity.

Atmospheric air is composed of approximately 21% oxygen and 79% nitrogen, with trace concentrations of other gases like carbon dioxide and argon. While oxygen is vital for life, it is a highly reactive compound and the primary agent in spoilage of packaged goods.

In simple terms, the OTR dictates how rapidly oxygen can penetrate the packaging material from the outside atmosphere to the product inside. This rate is typically expressed in cc / m² / day (cubic centimeters of oxygen per square meter per day). Critically, the lower this OTR value, the more effective the material is as an oxygen barrier.

As a practical benchmark, the industry generally classifies materials with an OTR value lower than 15.5 cc/m²/day (or 1 cc/100 in²/24 hr) as a high oxygen barrier.

OTR Relevance to Package Performance

The barrier integrity defined by a package’s OTR performance is vital because exposure to oxygen accelerates the degradation of various sensitive products.

• Food Preservation: Oxygen facilitates oxidation and rancidity—reactions that spoil fats and oils and produce stale flavors and odors. In fresh produce, oxygen can hasten ripening and decay. For sensitive items like coffee, high OTR leads to rapid loss of volatile aromatic compounds.
• Shelf Life: A superior (low) OTR directly correlates with extended product shelf life. By limiting oxygen ingress, the packaging helps preserve original flavor, color, texture, and nutritional profile.
• Pharmaceutical Integrity: For medical devices and sensitive drugs, maintaining an appropriate barrier prevents oxygen from chemically degrading active pharmaceutical ingredients, ensuring safety and effectiveness.

Visualizing the Barrier Difference

Flexible Packaging Methods for Oxygen Control

The primary objective of advanced flexible packaging is to establish a protected environment around the product. This control is commonly achieved through two main preparation methods:

1. Vacuum Packaging

Vacuum packaging removes air (and oxygen) from the package before it is tightly sealed.

• External Vacuum: A nozzle draws air out and the package is sealed outside the main unit.
• Chamber Vacuum: The package and surrounding air are placed in a chamber where atmospheric pressure is lowered before sealing.

Removing air is an effective initial step, but the duration of protection depends entirely on the material’s OTR and seal integrity. A poor barrier film will permit slow but steady re-entry of oxygen and will undermine the vacuum’s protective effect.

2. Modified Atmosphere Packaging (MAP)

MAP replaces the ambient air inside the package with a specific gas blend—often carbon dioxide or nitrogen—to slow microbial, enzymatic, and chemical deterioration.

• Process: After product loading, a gas-flushing process introduces the custom mixture to purge oxygen. The package is then sealed immediately.
• Requirement: To maintain the engineered atmosphere, the package must have an adequate oxygen barrier and robust seal integrity. MAP solutions require exceptionally low OTR to prevent atmosphere loss and ambient oxygen ingress.

Critical Barrier Materials

Achieving very low OTR values requires using polymers with exceptional gas-blocking properties. Common high-performance materials include:

Nylon (Polyamide or PA)

Nylon provides a balance of moderate barrier performance and mechanical toughness. Its high puncture resistance and lowered gas transmission make it a frequent choice as a structural layer in multi-layer films—often superior to commodity plastics such as polyethylene.

Ethylene Vinyl Alcohol (EVOH)

EVOH is widely regarded as the gold standard for high-barrier flexible applications. It offers exceptionally low oxygen permeability. Because EVOH is sensitive to moisture (which degrades its barrier properties), it is typically used as a very thin core layer co-extruded or laminated within a multi-layer film and protected by outer moisture-barrier layers.