A sheet packaging material (M, M', M", M′′′) for producing a sealed package of a pourable food product, comprising: - at least one first crease line (65; 66) and at least one second crease line (68; 69); - at least one third crease line (63; 67) which intersects said first crease line (65; 66) in at least one first point (91; 94; 101; 104) and said second crease line (68; 69) in at least one second point (92; 93; 102; 103); - at least one fourth crease line (61; 62) transverse to said first crease line (65; 66) and to said second crease line (68; 69); - at least one fifth crease line (70, 73; 74, 77), which extends between said first point (91, 94; 101, 104) and said fourth crease line (61; 62); - at least one sixth crease line (71, 72; 75, 76), which extends between said second point (92, 93; 102, 103) and said fourth crease line (61; 62); and - at least one panel (160, 161; 170, 171) bounded by said fifth crease line (70, 73; 74, 77), said sixth crease line (71, 72; 75, 76) and a portion of said third crease line (63; 67) interposed between said first point (91; 94; 101; 104) and said second point (92, 93; 102, 103); said panel (160, 161; 170, 171) being adapted to define at least part of a first folded flap (26; 32) of said finished package once said sheet packaging material (M, M', M", M′′′) has been folded; - said first point (91; 94; 101; 104) and said fourth crease line (61; 62) being spaced by a first distance H1; - said second point (92, 93; 102, 103) and said fourth crease line (61; 62) being spaced by a second distance H2; - said first point (91; 94; 101; 104) and said second point (92, 93; 102, 103) being spaced by a further distance; characterized in that the sum of said first distance H1 and said second distance H2 is less than said further distance. - at least one first crease line (65; 66) and at least one second crease line (68; 69); - at least one third crease line (63; 67) which intersects said first crease line (65; 66) in at least one first point (91; 94; 101; 104) and said second crease line (68; 69) in at least one second point (92; 93; 102; 103); - at least one fourth crease line (61; 62) transverse to said first crease line (65; 66) and to said second crease line (68; 69); - at least one fifth crease line (70, 73; 74, 77), which extends between said first point (91, 94; 101, 104) and said fourth crease line (61; 62); - at least one sixth crease line (71, 72; 75, 76), which extends between said second point (92, 93; 102, 103) and said fourth crease line (61; 62); and - at least one panel (160, 161; 170, 171) bounded by said fifth crease line (70, 73; 74, 77), said sixth crease line (71, 72; 75, 76) and a portion of said third crease line (63; 67) interposed between said first point (91; 94; 101; 104) and said second point (92, 93; 102, 103); said panel (160, 161; 170, 171) being adapted to define at least part of a first folded flap (26; 32) of said finished package once said sheet packaging material (M, M', M", M′′′) has been folded; - said first point (91; 94; 101; 104) and said fourth crease line (61; 62) being spaced by a first distance H1; - said second point (92, 93; 102, 103) and said fourth crease line (61; 62) being spaced by a second distance H2; - said first point (91; 94; 101; 104) and said second point (92, 93; 102, 103) being spaced by a further distance;