A reinforcing structure made of a sheet-like cellular base material which comprises material attenuations (3) in a distribution over its area in a view from above, wherein the material attenuations sub-divide the base material into a multitude of material islands (1R; 1T) which are delineated from each other by the material attenuations (3) but are still connected to each other, wherein (a) the material islands (1R; 1T) are convex base polygons in a view from above; (b) a respective plurality of the material islands (1R; 1T) jointly form a convex and preferably regular compound polygon (1H) in a view from above; and (c) the compound polygons (1H) differ, in their number of corners and/or in a ratio of the lengths of their sides, from the base polygons which form the material islands (1R; 1T).