This means that the benefits obtained from the integration of some polymeric etc. foam inside the panel are not considered here. Three core geometries have been considered in this report: I core with straight webs, O-core with rectangle shaped beams as a core and VfVV-core with hat or corrugated sheets as a core. These core geometries are presented in Figure 2. The stiffness properties for O- and VFv-panels are derived in this report.