is between 440 g l and 450 g l the content of sulphuric acid p1 is between 0 2 g l and 0 25 g l and the bath temperature is t3 where t3 is equal to or greater than 32 u00b0 c and less than 38 u00b0 c the remaining processing stages and technical conditions are identical to those in example 1 the pure protein used in this case is the phytoprotein isolated and extracted by the grinding degreasing and soaking of rapeseed the extracted protein being dissolved in distilled water resulting in a protein concentration as of between 4 and 8 by dissolving polyvinyl alcohol in distilled water for 1 5 hours at a temperature t1 of between 60 u00b0 c and 80 u00b0 c an aqueous solution with a concentration bs is obtained where bs is equal to or greater than 8 and less than 15 mixing the above two solutions in a certain proportion with pure protein forming a parts of the total pure protein and polyvinyl alcohol where a is 21 parts and with polyvinyl alcohol forming b parts of the total where b is 79 parts and by adding borax and mixing at a temperature t4 of between 40 u00b0 c and 90 u00b0 c the spinning dope is obtained the spinning dope of a viscosity measured by a gravitational flow viscosimeter of between 34 and 150 seconds is subjected to static deaeration by standing at a temperature tj of between 50 u00b0 c and 70.