and the structure of the core bar correspond to those of fig4 and fig6 however the cross section of the lattice cells 7 4 is circular here the walls and wall reinforcements 7 2 and 7 3 respectively interpenetrate intersect each other at a in the manner described above in accordance with the invention fig8 a is a side view as for example would be seen in direction of arrow a in fig1 of a core material 8 1 with a core height h fig8 b is a perspective illustration of a lattice cell 8 4 of the core material 8 1 the reinforcing fibres ribbons or strips 8 2 which form the lattice cell walls as well as the lattice cell walls 8 3 between adjacent lattice cells which interpenetrate each other as described above are not aligned perpendicularly at an angle of 90 u00b0 in relation to the boundary face z z of the core material or core bar instead they slope at an angle u03b3 to meet the boundary face z z obliquely fig9 comprises a plan view as for example would be seen in direction of arrow c in fig1 and three sectional illustrations d d e e and f f of a core material 9 1 which consists of core bars 9 1 1 9 1 2 r and 9 1 2 l 9 1 3 r and 9 1 3 l core bars 9 1 2 r and 9 1 2 l.