is the steady-state rate of oxygen permeation through the membrane at a specified temperature and relative humidity. Values are given in cc/100, in US standard units, 2/24 hr, and in metric (or SI) units as cc/m 2 /24 hr. Standard test conditions are 73°F (23°C) and 0% RH.

At a selected temperature and humidity, a barrier film is sealed between a chamber containing oxygen and a chamber void of oxygen. A coulometric sensor measures the oxygen that is transmitted through the material.

Correlation with package performance
The air we breathe is about 21% oxygen and 79% nitrogen, with very small amounts of other gases like carbon dioxide and argon. Oxygen is vital to human and animal life, and it is also a reactive compound that is a key factor in food spoilage: most chemical and biological reactions that produce rancid oils, molds, and flavor changes require oxygen to occur. So it's no surprise that food packaging (and some non-food packaging for products where atmospheric oxygen poses a hazard) has progressed and found ways to reduce oxygen exposure and extend the shelf life of oxygen-sensitive products.
There are two ways to reduce product exposure to oxygen through flexible packaging:
1. Modified Atmosphere Packaging (MAP) is the process of replacing the air in the headspace of the package with another gas before final sealing. This modified atmosphere packaging is firmly established in the food industry and continues to grow in importance. In short, the natural environment air in the package is replaced by a gas or gas mixture (usually nitrogen and carbon dioxide). This packaging in a protective atmosphere maintains the quality of fresh food for a longer period of time, extends shelf life and enables food producers to geographically capture a larger market for perishable products. As well as products for meat and sausage products, dairy products, bread, fruits and vegetables, fish or convenience products.