The polymer nanofibres containing polar groups are brought into contact with a solution of at least one natural and/or semi-synthetic and/or synthetic tannin/tannins in a polar solvent, while the weight ratio of the polymer nanofibres to tannin/tannins in the solution is at least 1:0.01. Between the polar groups of the polymer nanofibres and the phenolic groups of the tannin/tannins, there are spontaneously formed hydrogen bonds and the tannin/tannins are stored in the layer on the surface of the polymer nanofibres, whereby the textile fibres are stiffened and strengthened. The invention also relates to the layer of the polymer nanofibres with the immobilized tannin/tannins, in which there is/are the tannin/tannins placed in the layer on the surface of the polymer nanofibres by means of the hydrogen bonds between the polar groups of the polymer nanofibres and the phenolic groups of tannin/tannins.
