Surface at the top of the containers, i.e. the lid or cap, is assumed to be impermeable and is not included in the calculations of OTR/WVTR. The wall and layer thickness of the container, laminates or IML barrier film is assumed constant throughout article surface. Calculations are based on an empty container.

For OTR, the oxygen level inside container is initially assumed to be 0 Vol %. The humidity can be varied as input parameter. Steady state condition of permeation. The amount of permeant passing through each layer is identical, and equal to the amount passing through the total structure. Diffusion takes place in one direction only. 

The concentration distance relationship through the polymer is linear. The permeability coefficient is assumed to be a constant of the material and not dependent on sample thickness.