A sheet packaging material (1, 1', 1", 1''') for producing a sealed package containing a pourable product; said sheet packaging material (1, 1', 1", 1''') comprising two first boundary edges (3, 4) parallel to a longitudinal direction and two second boundary edges (5, 6) parallel to a transversal direction orthogonal to said longitudinal direction; said sheet packaging material (1, 1', 1", 1''') comprising at least a bottom transversal crease line (7, 7", 7''') and a top transversal crease line dividing said sheet packaging material (1, 1', 1", 1''') into: - a bottom region containing a bottom crease pattern (11, 11', 11", 11''') and configured to form a bottom portion of said package including a bottom panel; - a top region containing a top crease pattern; and - an intermediate region contained between said bottom transversal crease line (7, 7", 7''') and said top transversal crease line and interposed between said bottom region and said top region, with respect to said longitudinal direction (A; said bottom transversal crease line (7, 7", 7''') including: - a bottom central portion (7a, 7a", 7a'''); - at least one bottom end portion (7b, 7b", 7b''') arranged on one side of said bottom central portion (7a, 7a", 7a''') and adjacent to one of said first boundary edges (3, 4); and - at least one bottom side portion (7c, 7c", 7c'''), adjacent to one side of said bottom central portion (7a, 7a", 7a''') and extending between said bottom central portion (7a, 7a", 7a''') and said at least one bottom end portion (7b, 7b", 7b'''); said bottom crease pattern (11, 11', 11", 11''') including at least a pair of slanted crease lines (20, 21; 20", 21") inclined relatively to both said longitudinal direction and said transversal direction and extending within said bottom region; wherein said slanted crease lines (20, 21; 20", 21") have first ends pointing to one of said second boundary edges (5, 6) and second ends pointing to a continuous line parallel to said transversal direction and including said bottom central portion (7a, 7a", 7a''') and said at least one bottom end portion (7b, 7b", 7b''') of said bottom transversal crease line (7, 7", 7'''); said slanted crease lines (20, 21; 20", 21") delimiting, together with said at least one bottom side portion (7c, 7c", 7c'''), a flap area of said sheet packaging material (1, 1', 1", 1''') designed to form at least part of a lateral flap of said package; wherein a projection of each slanted crease line (20, 21; 20", 21") on said continuous line along a respective direction parallel to said slanted crease line (20, 21; 20", 21") identifies on said continuous line one respective first point; said bottom crease pattern (11, 11', 11", 11''') further including at least a pair of longitudinal crease lines (19a, 19b; 19a', 19b'; 19a", 19b") extending within said bottom region, arranged at opposite sides of said flap area relatively to said transversal direction, and defining together a folding line about which said lateral flap is designed to be folded inwardly towards said bottom panel; characterized in that a projection of each longitudinal crease line (19a, 19b; 19a', 19b'; 19a", 19b") on said continuous line along a respective direction parallel to said longitudinal crease line (19a, 19b; 19a', 19b'; 19a", 19b") identifies on said continuous line one respective second point, said second point being arranged at one side of said flap area and being spaced, along said transversal direction, from the corresponding first point arranged at the same one side of said flap area by a transversal offset. - a bottom region containing a bottom crease pattern (11, 11', 11", 11''') and configured to form a bottom portion of said package including a bottom panel; - a top region containing a top crease pattern; and - an intermediate region contained between said bottom transversal crease line (7, 7", 7''') and said top transversal crease line and interposed between said bottom region and said top region, with respect to said longitudinal direction (A; - a bottom central portion (7a, 7a", 7a'''); - at least one bottom end portion (7b, 7b", 7b''') arranged on one side of said bottom central portion (7a, 7a", 7a''') and adjacent to one of said first boundary edges (3, 4); and - at least one bottom side portion (7c, 7c", 7c'''), adjacent to one side of said bottom central portion (7a, 7a", 7a''') and extending between said bottom central portion (7a, 7a", 7a''') and said at least one bottom end portion (7b, 7b", 7b''');