Process for preparing a material useful for the production of HME filters, which comprises the following steps: a) preparing an acidic aqueous solution of chitosan in a concentration from 1 to 2.5% by weight; b) preparing an aqueous solution of a gelatin of animal origin in a concentration from 2.5 to 5% by weight, operating at a temperature between 40 and 50 °C; c) mixing the two solutions thus obtained in such quantities as to obtain a weight ratio gelatin:chitosan from 80:20 to 50:50, preferably 70:30, gently stirring the resulting solution to avoid the formation of a foam until obtaining a homogeneous solution, and subsequently diluting the mixture to obtain a total polymer concentration of from 2 to 4%, preferably 2%, by weight; d) pouring the solution prepared in step c) into a container with the bottom made of a material having thermal conductivity greater than or equal to 15 W/(m·K) and side walls made of a material having thermal conductivity less than or equal to 1 W/(m·K); e) freeze-drying, inside said container, the solution obtained in step c) according to the following phases: - freezing the hydrogel to a temperature of from -20 to -60 °C, preferably -40 °C, carried out by placing the bottom of the container in contact with a refrigerating system; - primary drying by heating with a speed between 2 and 8 °C/h up to a temperature between -5 and -10 °C, operating at a pressure between 0.001 mbar and atmospheric pressure; - secondary drying by heating with a speed between 1 and 5 °C/h up to a temperature between 15 and 20 °C, operating at a pressure between 0.001 mbar and atmospheric pressure; f) subjecting the freeze-dried product obtained in step e) to a crosslinking treatment by thermal dehydration, by heating it to a temperature from 140 to 160 °C, preferably 160 °C, at a pressure between 0.001 mbar and the atmospheric pressure and for a duration between 24 and 48h. a) preparing an acidic aqueous solution of chitosan in a concentration from 1 to 2.5% by weight; b) preparing an aqueous solution of a gelatin of animal origin in a concentration from 2.5 to 5% by weight, operating at a temperature between 40 and 50 °C; c) mixing the two solutions thus obtained in such quantities as to obtain a weight ratio gelatin:chitosan from 80:20 to 50:50, preferably 70:30, gently stirring the resulting solution to avoid the formation of a foam until obtaining a homogeneous solution, and subsequently diluting the mixture to obtain a total polymer concentration of from 2 to 4%, preferably 2%, by weight; d) pouring the solution prepared in step c) into a container with the bottom made of a material having thermal conductivity greater than or equal to 15 W/(m·K) and side walls made of a material having thermal conductivity less than or equal to 1 W/(m·K); e) freeze-drying, inside said container, the solution obtained in step c) according to the following phases: - freezing the hydrogel to a temperature of from -20 to -60 °C, preferably -40 °C, carried out by placing the bottom of the container in contact with a refrigerating system; - primary drying by heating with a speed between 2 and 8 °C/h up to a temperature between -5 and -10 °C, operating at a pressure between 0.001 mbar and atmospheric pressure; - secondary drying by heating with a speed between 1 and 5 °C/h up to a temperature between 15 and 20 °C, operating at a pressure between 0.001 mbar and atmospheric pressure; - freezing the hydrogel to a temperature of from -20 to -60 °C, preferably -40 °C, carried out by placing the bottom of the container in contact with a refrigerating system; - primary drying by heating with a speed between 2 and 8 °C/h up to a temperature between -5 and -10 °C, operating at a pressure between 0.001 mbar and atmospheric pressure; - secondary drying by heating with a speed between 1 and 5 °C/h up to a temperature between 15 and 20 °C, operating at a pressure between 0.001 mbar and atmospheric pressure; f) subjecting the freeze-dried product obtained in step e) to a crosslinking treatment by thermal dehydration, by heating it to a temperature from 140 to 160 °C, preferably 160 °C, at a pressure between 0.001 mbar and the atmospheric pressure and for a duration between 24 and 48h.