Fibrous material is treated with an organic hydrazide and nitrous acid and subsequently dried. The nitrous acid, in the form of an alkali metal nitrite, may be applied to the material together with the hydrazide in the same aqueous solution, and the impregnated material dried and treated with an acid to liberate the nitrous acid, or the material may be impregnated with an aqueous solution of an acid salt of the hydrazide and subsequently treated with an aqueous solution of the nitrite. Between these steps the material may be dried, with or without tension, at temperatures up to 125 DEG C. The impregnations may be effected at temperatures between 0 DEG C. and 100 DEG C. After drying, the impregnated material may be baked at temperatures from 50 DEG to 200 DEG C. The hydrazide is presumed to react with the nitrous acid within the fibres to form the corresponding azide, and the azide is presumed to decompose upon heating to form the corresponding isocyanate. Urea, dithiourea, acetamide, benzene sulphonamide, p-toluene sulphonamide, cyanamide, guanidine, aminoguanidine or softeningagents may be included in the solution containing the hydrazide, and formaldehyde may be added either to the hydrazide solution or the nitrite solution or to the solution containing the nitrite and hydrazide. The hydrazide may be the dihydrazide of succinic, glutaric, adipic or sebacic acid, hexadecane-1:16-dicarboxylic acid dihydrazide, benzoic acid hydrazide, isophthalic acid dihydrazide, citric acid trihydrazide, stearic acid hydrazide, hydroxy-stearic acid hydrazide or polyacrylic acid polyhydrazide, and these may be used as such or as hydrochlorides. The materials treated may be fabrics of cotton, viscose rayon, cellulose acetate, nylon, polyethylene terephthalate, or natural or regenerated protein fibres or paper. In examples: (2) a cotton fabric is immersed in an aqueous dispersion containing sebacic acid dihydrazide, sodium nitrite and the disodium salt of methylene dinaphthalene sulphonic acid, squeezed to 75 per cent by weight take-up, dried at 50 DEG C., impregnated in an aqueous solution of acetic acid, dried at 20 DEG to 30 DEG C., glazed on a calendar at 200 DEG C., heated at 150 DEG C. for 3 minutes and washed in soap solution and then in water; (4) a viscose rayon staple fibre fabric is immersed in an aqueous solution of sebacic acid dihydrazide dihydrochloride, squeezed to 75 per cent by weight take-up, dried at 20 DEG to 50 DEG C., immersed in an aqueous solution of sodium nitrite, squeezed to 75 per cent by weight take-up, stretched to its original dimensions on a pin stenter and dried and baked in an oven at 150 DEG C.; (5) a sheet of absorbent paper is passed through an aqueous solution of sebacic acid dihydrazide dihydrochloride, squeezed to 200 per cent by weight take-up, dried at 100 DEG C., impregnated with an aqueous solution of sodium nitrite, dried and baked at 120 DEG C.; (6) a viscose rayon staple fibre fabric is impregnated with an aqueous solution containing sebacic acid dihydrazide dihydrochloride and acetamide, squeezed to a take-up of 75 per cent by weight, dried on a pin stenter at 100 DEG C., sprayed while on the stenter with an aqueous solution of sodium nitrite and dried and baked in an oven at 125 DEG C. while on the stenter frame; (10) a mercerized cotton gaberdine fabric is impregnated with an aqueous solution containing sebacic acid dihydrazide dihydrochloride and 11-hydroxystearic acid hydrazide hydrochloride at 80 DEG C., squeezed to a take-up of 60 per cent by weight, air-dried, impregnated with an aqueous solution containing formaldehyde and sodium nitrite at 20 DEG C. and rinsed in warm water; (14) a cotton fabric is immersed in an aqueous solution of sebacic acid dihydrazide dihydrochloride, squeezed to 75 per cent by weight take-up, impregnated with an aqueous solution of sodium nitrite, squeezed to 100 per cent by weight take-up, conditioned to contain 10 per cent by weight of moisture, embossed and heated at 140 DEG C. or conditioned at room temperature for 24 hours; (18) a cloth made from polyethylene terephthalate yarn is padded with an aqueous solution containing sebacic acid dihydrazide dihydrochloride and stearic acid hydrazide hydrochloride at 80 DEG C., squeezed to a take-up of 35 per cent by weight, dried at 50 DEG to 60 DEG C., padded with an aqueous solution of sodium nitrite at 20 DEG C., squeezed and heated at 120 DEG C.; (19) a polyamide cloth is padded with an aqueous solution containing sebacic acid dihydrazide dihydrochloride and 11-hydroxystearic acid hydrazide hydrochloride, squeezed to a take-up of 45 per cent by weight, air-dried, padded with an aqueous solution containing formaldehyde and sodium nitrite, squeezed to a 45 per cent by weight take-up and heated at 125 DEG C.ALSO:Fabrics are treated with an organic hydrazide and nitrous acid and subsequently dried. The nitrous acid, in the form of an alkali metal nitrite, may be applied to the material together with the hydrazide in the same aqueous solution, and the impregnated material dried and treated with an acid to liberate the nitrous acid, or the material may be impregnated with an aqueous solution of an acid salt of the hydrazide and subsequently treated with an aqueous solution of the nitrite. Between these steps the material may be dried, with or without tension, at temperatures up to 125 DEG C. The impregnations may be effected at temperatures between 0 DEG C. and 100 DEG C. After drying, the impregnated material may be baked at temperatures from 50 DEG C. to 200 DEG C. The hydrazide is presumed to react with the nitrous acid within the fibres to form the corresponding azide, and the azide is presumed to decompose upon heating to form the corresponding isocyanate. Urea, dithiourea, acetamide, benzene sulphonamide, p - toluene sulphonamide, cyanamide, guanidine, aminoguanidine or softening agents may be included in the solution containing the hydrazide, and formaldehyde may be added either to the hydrazide solution or the nitrite solution or to the solution containing the nitrite and hydrazide. Fabrics treated according to the process may be subjected to a subsequent calendering, embossing, beetling, rippling, pressing or Schreinering operation. The hydrazide may be the dihydrazide of succinic, glutaric, adipic or sebacic acid, hexadecane - 1 : 16 - dicarboxylic acid dihydrazide, benzoic acid hydrazide, isophthalic acid dihydrazide, citric acid trihydrazide, stearic acid hydrazide, hydroxy - stearic acid hydrazide or polyacrylic acid polyhydrazide, and these may be used as such or as hydrochlorides. The materials treated may be fabrics of cotton, viscose rayon, cellulose acetate, nylon, polyethylene terephthalate, or natural or regenerated protein fibres. In examples, (2) a cotton fabric is immersed in an aqueous dispersion containing sebacic acid dihydrazide, sodium nitrite and the disodium salt of methylene dinaphthalene sulphonic acid, squeezed to 75 per cent by weight take-up, dried at 50 DEG C., impregnated in an aqueous solution of acetic acid, dried at 20 DEG to 30 DEG C., glazed on a calender at 200 DEG C., heated at 150 DEG C. for 3 minutes and washed in soap solution and then in water; (4) a viscose rayon staple fibre fabric is immersed in an aqueous solution of sebacic acid dihydrazide dihydrochloride, squeezed to 75 per cent by weight take-up, dried at 20 DEG to 50 DEG C., immersed in an aqueous solution of sodium nitrite, squeezed to 75 per cent by weight take-up, stretched to its original dimensions on a pin stenter and dried and baked in an oven at 150 DEG C.; (6) a viscose rayon staple fibre fabric is impregnated with an aqueous solution containing sebacic acid dihydrazide dihydrochloride and acetamide, squeezed to a take-up of 75 per cent by weight, dried on a pin stenter at 100 DEG C., sprayed while on the stenter with an aqueous solution of sodium nitrite and dried and baked in an oven at 125 DEG C. while on the stenter frame; (10) a mercerized cotton gaberdine fabric is impregnated with an aqueous solution containing sebacic acid dihydrazide dihydrochloride and 11 - hydroxystearic acid hydrazide hydrochloride at 80 DEG C., squeezed to a take-up of 60 per cent by weight, air-dried, impregnated with an aqueous solution containing formaldehyde and sodium nitrite at 20 DEG C., squeezed to a take-up of 60 per cent by weight, baked at 130 DEG C. and rinsed in warm water; (14) a cotton fabric is immersed in an aqueous solution of sebacic acid dihydrazide dihydrochloride, squeezed to 75 per cent by weight take-up, impregnated with an aqueous solution of sodium nitrite, squeezed to 100 per cent by weight take-up, conditioned to contain 10 per cent by weight of moisture, embossed and heated at 140 DEG C. or conditioned at room temperature for 24 hours; (18) a cloth made from polyethylene terephthalate yarn is padded with an aqueous solution containing sebacic acid dihydrazide dihydrochloride and stearic acid hydrazide hydrochloride at 80 DEG C., squeezed to a take-up of 35 per cent by weight, dried at 50 DEG to 60 DEG C., padded with an aqueous solution of sodium nitrite at 20 DEG C., squeezed and heated at 120 DEG C.; (19) a polyamide cloth is padded with an aqueous solution containing sebacic acid dihydrazide dihydrochloride and 11-hydroxystearic acid hydrazide hydrochloride, squeezed to a take-up of 45 per cent by weight, air-dried, padded with an aqueous solution containing formaldehyde and sodium nitrite, qsueezed to a 45 per cent by weight take-up and heated at 125 DEG C.