The mechanical properties in the thickness direction of the material were defined by three different tests: creep test, monotonic loading and compressibility tests according to IEC 60641-2 [5]. All tests were performed on a stack of six pieces of milled material. The test pieces were separated by 0.2 mm thick stainless steel plates in order to reduce the effect of surface entanglement. The test pieces were then placed between two smooth steel plates and compressed using an MTS universal testing machine. The value of the loading speed was 5min/mm, and it was chosen according to [5]. In the creep tests the load was kept at a constant level throughout the entire experiment. The deformation of the test pieces was measured by three inductive displacement transducers (HBM type K-WA 10mm). The displacement transducers were fixed on the upper loading plate and placed radially around the test pieces. The load was measured by a load cell with maximum load of 100 kN