Due to the fact that not any of the usually used materials like Precision board is available in Germany, I use Necuron 480 HDU. It has a density of 0.48g/cm³ this equals the 30lb/ft³ Precision board which is prefered by Dan.
I contacted Necumer in Germany and got immediately a box with samples of different degrees of hardness. I have made a few test cuts and decided that Necuron 480 will be the best for my assignment and bought a few 1500mm x 500mm sheets in different thicknesses.
Maybe this will be of interest for people in countries who have only limited or no access to materials used in Canada or the USA.