For 3D blow molding models solved using shell elements, Ansys Polyflow can also
compute the permeability of the blown product. This calculation is useful in the
packaging of pharmaceuticals, where the moisture barrier is an essential property.
The permeability is known to be inversely proportional to the local thickness
. Given the permeability coefficient 
, the permeability per unit area can be evaluated as
 | (17–23) |
If the material involves several overlapping layers, the permeability per unit area is computed from
 | (17–24) |
where 
is the thickness of the 
th layer, and 
is the corresponding permeability coefficient.
The total permeability for the blown product is computed from
 | (17–25) |
The permeability coefficient denotes a given amount of water passing through a
sheet of material with a given thickness and area, during a given time. Typical
values for 
are on the order of 10-11 to
10-12 g-mm/s/mm2. See
Inputs for Computing the Permeability of the Blown Product for
details about setting up the calculation.