In automotive industry acoustic trim materials are widely used in order to reach passenger comfort targets. The dynamic behaviour of the poro-elastic materials is typically modelled by the Biot theory, which however leads to expensive numerical finite element calculations for sound packages containing foam layers coupled to heavy damping layers. One way to deal with it is to use the sub-structuring Patch-Transfer-Function (PTF) method, which couples subdomains at their interfaces through impedance relations. In the literature this approach was already applied to structure-cavity systems including locally reacting poro-elastic materials. In this paper a methodology is presented allowing to numerically assess the PTF impedance matrices of non-locally reacting trim materials using the Biot based poro-elastic finite element method (FEM). The layered trim consisted of a poro-elastic liner covered by an impervious visco-elastic heavy layer which is representative for typical automotive applications. Simplifications of these trim impedance matrices are introduced resulting in considerable calculation cost reductions. Here a patch in the centre of the trim material is excited and the transfer functions are used to build the trim impedance matrices. The first load case is a piston excitation of a foam layer patch and the second load case is a constant pressure excitation of a heavy layer patch. The associated prediction errors are discussed by means of a numerical case study. The numerical test case consisted of a clamped plate covered with a double layer trim radiating into a rectangular air cavity. It is shown that a considerable calculation time reduction may be achieved while keeping prediction accuracy at an acceptable level.