Any prediction of blow molding or thermoforming is based on a transient calculation. The melt undergoes deformations in time, and the process conditions (such as the closing speed of the mold and the inflation pressure) may also vary with time.

In 2D, an axisymmetric geometry is usually used in the Ansys Polyflow calculation, although a planar description can also be used. Such a representation enables calculation through the thickness, and therefore prediction of the possible local shear effects. This is also the case when running an actual 3D calculation. For thin 3D objects in 3D, a membrane element is used, since it allows for calculation of complex shapes at a moderate cost. This representation is suited for elongation-like deformations, but is unable to report shear deformations across the thickness.