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 (36, 38, 40) having a variation in structural strength such that at least one of the cell groups (36, 38, 40) has a structural strength that is not the same as the remaining cell groups (36, 38, 40); 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 (36, 38, 40) having a variation in structural strength such that at least one of the cell groups (36, 38, 40) has a structural strength that is not the same as the remaining cell groups (36, 38, 40); 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.