A structural panel made by a layer-by-layer additive manufacturing process for use in a gas turbine engine, the panel comprising: a first exterior wall including: a first exterior surface ; and a first interior surface parallel to the first exterior surface ; a second exterior wall including: a second exterior surface ; and a second interior surface parallel to the second exterior surface ; and a plurality of interior walls extending from the first interior surface to the second interior surface , the interior walls arranged to form a pattern of hexagonal cells ; wherein the pattern of hexagonal cells includes a plurality of cell groups having a variation in structural strength such that at least one of the cell groups has a structural strength that is not the same as the remaining cell groups ; characterised in that : some of the interior walls include one aperture , others of the interior walls include more than one aperture , and still others of the interior walls include no apertures ; and the first exterior wall further includes a plurality of effusion cooling holes extending through the first exterior wall between the first interior surface and the first exterior surface , and the second exterior wall further includes at least one cooling air hole extending through the second exterior wall between the second interior surface and the second exterior surface . a first exterior wall including: a first exterior surface ; and a first interior surface parallel to the first exterior surface ; a first exterior surface ; and a first interior surface parallel to the first exterior surface ; a second exterior wall including: a second exterior surface ; and a second interior surface parallel to the second exterior surface ; and a second exterior surface ; and a second interior surface parallel to the second exterior surface ; and a plurality of interior walls extending from the first interior surface to the second interior surface , the interior walls arranged to form a pattern of hexagonal cells ; wherein the pattern of hexagonal cells includes a plurality of cell groups having a variation in structural strength such that at least one of the cell groups has a structural strength that is not the same as the remaining cell groups ; characterised in that : some of the interior walls include one aperture , others of the interior walls include more than one aperture , and still others of the interior walls include no apertures ; and the first exterior wall further includes a plurality of effusion cooling holes extending through the first exterior wall between the first interior surface and the first exterior surface , and the second exterior wall further includes at least one cooling air hole extending through the second exterior wall between the second interior surface and the second exterior surface . some of the interior walls include one aperture , others of the interior walls include more than one aperture , and still others of the interior walls include no apertures ; and the first exterior wall further includes a plurality of effusion cooling holes extending through the first exterior wall between the first interior surface and the first exterior surface , and the second exterior wall further includes at least one cooling air hole extending through the second exterior wall between the second interior surface and the second exterior surface . <EOS>