Abstract: A method for forming an undergarment having side seams from a two-dimensional preform comprises the steps of cutting a continuous web along transverse cut lines to form individual preforms; cutting each preform along a leg contour extending along each longitudinal side of the preform in the region of a central section, wherein each leg contour does not touch the respective longitudinal side, thus forming two gripping flaps; gripping the preform at the gripping flaps; pulling the gripping flaps outwardly away from the longitudinal sides such that the preform is doubled over along a transverse centerline and such that sealing areas in the region of back waist sections are placed in a superimposed relationship with sealing areas in the region of front waist sections; mutually connecting the sealing areas.