elements 1 of fig1 2 5 and 6 fig8 shows the raw side 105 of a medium section 120 of the filter medium 106 that extends between two fold edges f the fold edges f are embossed as folding lines in the unfolded filter medium 106 in the folded filter medium 106 the fold tips 102 surround the fold edges f on the filter medium 106 a plurality of elongate adhesive sections 122 extends along straight lines of adhesive 101 the lines of adhesive 101 extend equidistantly parallel to each other and perpendicularly to the fold edges f a spacing 132 between two neighboring lines of adhesive 101 is approximately 25 mm respectively along each of the lines of adhesive 101 two interruptions 107 of the adhesive of identical length are arranged between the adhesive sections 122 the width 134 of the interruptions 107 of the adhesive perpendicular to the fold edges f is approximately 15 mm the interruptions 107 of the adhesive of neighboring lines of adhesive 101 viewed in the direction of the fold edges f are displaced relative to each other the adhesive sections 122 of neighboring lines of adhesive 101 delimit each a passage part 124 of a passage that extends in the raw side intermediate fold space 148 a of the folded filter medium 106 between the fold edges f similar to the embodiment to be explained farther down in connection with fig1 the interruptions 107 of the adhesive connect the respective neighboring passage parts 124 the interruptions 107 of the adhesive of the neighboring lines of adhesive 101 realize two passages 126 that in the embodiment shown in fig8 are extending.