50 g of polyhexamethylene adipamide fibers of 1 0 mm length and a titre of 3 3 decitex are stirred for 20 minutes in 1 liter of an aqueous solution of 60 u00b0 c containing 0 5 g tannin 1 0 g potassium aluminum sulphate and 10 g ammonium sulphate the ph of the solution is 4 0 the fibers are centrifuged and dried at 22 u00b0 c they have a specific electric conductivity of 2 5 u00d7 10 sup 8 ohm cm sup 1 the fibers possess good flow and gliding properties and a very good spring capacity in an electrostatic field at 30 80 relative air humidity when heated for 10 minutes to 150 u00b0 c and cooled again to room temperature flow and gliding properties and the spring capacity of the fibers in an electrostatic field are as good as before 50 g of polycaprolactam fibers of 2 0 mm length and a titre of 22 decitex are stirred for 20 minutes in 1 liter of an aqueous solution of 60 u00b0 c containing 0 5 g tannin 1 0 g potassium aluminum sulphate and 10 g ammonium sulphate the ph of the solution is 4 0 the fibers are centrifuged and.