At least a second vent channel (14) is provided, connected through second vent openings (9) to the first vent channel, which includes third vent openings (12) venting into a second vent channel (14). At least one second vent channel (14) runs parallel to, or at right angles to the first (2). At least one further vent channel (14) is provided at at least one end of the sack. The end completion weld (11) of the sack at this end, borders the at least one second vent channel. At least one further second vent channel is provided at the other end of the sack. An independent claim is included for the corresponding method of manufacture.
