A manufacturing method for manufacturing a core for a sound-absorbing panel with sandwich structure for noise reduction in an aircraft, the method comprising the steps of: a) providing a plurality of first sheet-shaped partitioning elements, each first partitioning element having a plurality of vertical slits, which extend transversely from a respective first edge of each first partitioning element, the first partitioning elements further having a plurality of transverse slits extending along a direction transverse to the plurality of vertical slits of the first partitioning elements; b) providing a plurality of second sheet-shaped partitioning elements, each second partitioning element having a plurality of vertical slits, which extend transversely from a respective first edge of each second partitioning element; c) arranging the first partitioning elements on a work surface, spaced from each other, so that a second edge of each first partitioning element, opposite to said first edge of each first partitioning element, rests on said work surface; d) arranging the second partitioning elements on the first partitioning elements, transversely thereto, so that each vertical slit of the plurality of vertical slits of the second partitioning elements interlocks with a respective vertical slit of the plurality of vertical slits of a respective first partitioning element, so that the first partitioning elements and the second partitioning elements define between them a plurality of cells, each cell being delimited laterally by a pair of opposing first partitioning elements and a pair of opposing second partitioning elements; and e) arranging respective horizontal partitioning elements, preferably made of flexible material, through a pair of transverse slits of a respective pair of successive first partitioning elements. a) providing a plurality of first sheet-shaped partitioning elements, each first partitioning element having a plurality of vertical slits, which extend transversely from a respective first edge of each first partitioning element, the first partitioning elements further having a plurality of transverse slits extending along a direction transverse to the plurality of vertical slits of the first partitioning elements; b) providing a plurality of second sheet-shaped partitioning elements, each second partitioning element having a plurality of vertical slits, which extend transversely from a respective first edge of each second partitioning element; c) arranging the first partitioning elements on a work surface, spaced from each other, so that a second edge of each first partitioning element, opposite to said first edge of each first partitioning element, rests on said work surface; d) arranging the second partitioning elements on the first partitioning elements, transversely thereto, so that each vertical slit of the plurality of vertical slits of the second partitioning elements interlocks with a respective vertical slit of the plurality of vertical slits of a respective first partitioning element, so that the first partitioning elements and the second partitioning elements define between them a plurality of cells, each cell being delimited laterally by a pair of opposing first partitioning elements and a pair of opposing second partitioning elements; and e) arranging respective horizontal partitioning elements, preferably made of flexible material, through a pair of transverse slits of a respective pair of successive first partitioning elements.