A sheet packaging material for producing a sealed package comprises two first boundary edges parallel to a longitudinal direction and two second boundary edges parallel to a transversal direction orthogonal to the longitudinal direction. The sheet packaging material includes at least a bottom transversal crease line including a bottom central portion, a bottom end portion and a bottom side portion. The sheet packaging material includes a pair of slanted crease lines inclined relative to both the longitudinal and transverse directions. The slanted crease lines have first ends pointing to one of the second boundary edges and second ends pointing to a continuous line parallel to the transversal direction and including the bottom central portion and the bottom end portion. The slanted crease lines delimit, with the bottom side portion, a flap area of the sheet packaging material designed to form at least part of a lateral flap of the package.