A sheet packaging material (M, M') for producing a sealed package (1, 1') containing a pourable food product, said packaging material (M, M') having a rectangular or square configuration with two boundary edges parallel to a longitudinal direction and two other boundary edges (23, 24) parallel to a transversal direction orthogonal to said longitudinal direction; said packaging material (M, M') comprising at least two transversal crease lines (25, 26, 26') extending transversally to said longitudinal direction and dividing the packaging material (M, M') into: - a bottom region containing a bottom crease pattern and configured to form a bottom portion of said package (1, 1'); - a top region containing a top crease pattern and configured to form a top portion of said package (1, 1'); and - an intermediate region contained between said transversal crease lines (25, 26, 26'), interposed between said bottom region and said top region and designed to form a main portion of said package (1, 1') having a plurality of side wall portions; wherein said transversal crease lines (25, 26, 26') are configured to define a bottom peripheral edge and a top peripheral edge (9, 9') of said package (1, 1') respectively dividing said bottom portion and said top portion from said main portion; wherein said intermediate region further comprises a plurality of V-shaped crease lines having respective vertices located on or adjacent to at least a first transversal crease line (25, 26, 26') of the transversal crease lines (25, 26, 26') and at given points thereof destined to define the ends of respective lateral edge zones delimiting the side wall portions of said package (1, 1'); each said V-shaped crease line extending from and in proximity of said first transversal crease line (25, 26, 26') towards a second transversal crease line (26, 26', 25) of said transversal crease lines (25, 26, 26'); each said V-shaped crease line comprising two legs diverging from the respective vertex; said V-shaped crease lines being the only crease lines present in said intermediate region at the areas designed to define the lateral edge zones between the side wall portions of said package (1, 1'); characterized in that each said V-shaped crease line extends from said first transversal crease line (25, 26, 26') towards said second transversal crease line (26, 26', 25) and has a size, parallel to said longitudinal direction, greater than zero and smaller than one fourth of the total height of said intermediate region measured parallel to the longitudinal direction. - a bottom region containing a bottom crease pattern and configured to form a bottom portion of said package (1, 1'); - a top region containing a top crease pattern and configured to form a top portion of said package (1, 1'); and - an intermediate region contained between said transversal crease lines (25, 26, 26'), interposed between said bottom region and said top region and designed to form a main portion of said package (1, 1') having a plurality of side wall portions; wherein said transversal crease lines (25, 26, 26') are configured to define a bottom peripheral edge and a top peripheral edge (9, 9') of said package (1, 1') respectively dividing said bottom portion and said top portion from said main portion; wherein said intermediate region further comprises a plurality of V-shaped crease lines having respective vertices located on or adjacent to at least a first transversal crease line (25, 26, 26') of the transversal crease lines (25, 26, 26') and at given points thereof destined to define the ends of respective lateral edge zones delimiting the side wall portions of said package (1, 1'); each said V-shaped crease line extending from and in proximity of said first transversal crease line (25, 26, 26') towards a second transversal crease line (26, 26', 25) of said transversal crease lines (25, 26, 26'); each said V-shaped crease line comprising two legs diverging from the respective vertex; said V-shaped crease lines being the only crease lines present in said intermediate region at the areas designed to define the lateral edge zones between the side wall portions of said package (1, 1'); characterized in that each said V-shaped crease line extends from said first transversal crease line (25, 26, 26') towards said second transversal crease line (26, 26', 25) and has a size, parallel to said longitudinal direction, greater than zero and smaller than one fourth of the total height of said intermediate region measured parallel to the longitudinal direction.