a process and a device for producing bags from a strip of thermoplastic material wherein mated layers of foil strip are supplied to serially arranged bonding devices to provide bonded seams extending over the width of the layers at specific intervals corresponding to the width of the bags with said bonding devices being alternated with cooling means to lower the temperature of the bonded areas and thereafter advancing the material to a cutting device designed to separate the bags divided by the bonded seams from the chain of bags produced by the bonding operation .