the filaments 12 by means of a test arrangement with a copper wire of 0 12 mm diameter it was possible to measure and determine that for the production of a polypropylene non woven material pp with a filament titre of 2 dtex 1 dtex thickness of a filament of a weight of 1 g and a length of 10 000 m a draw off force of 0 2n is required the results of the measuring are shown in fig2 together with a schematic arrangement of the test lay out as can be seen the filament draw off force of 0 2n can be achieved easily with thirty stacked slot nozzles while with the use of only one slot nozzle a sufficient filament draw off force could not be achieved even when increasing the compressed air pressure the compressor as well as the slot nozzles 16 are operated polytropically the compressor compresses the air from the ambient state polytropically to or higher than the critical pressure of 1 894 bar in order to achieve as complete a use of the energy as well as the adiabatic process the compressor the supply lines and the backs of the slot nozzles are insulated although the compressed air has reached a relatively high temperature of to more than 350 k approximately room temperature is reached again at the exit of the slot nozzles 16 when the air is expanded and the pressure of the air decreased but the slot nozzles 16 heat up so that there can be danger of the filaments 12.