Fibrous materials of natural or regenerated cellulose or protein are waterproofed by treating them with substances containing an aliphatic, cycloaliphatic or aliphatic-aromatic radicle having at least 8 carbon atoms and at least one olefinic group in which the carbon double linkage is in conjugated position to doubly-attached oxygen or is present in a vinyl group, and heating to a temperature above 100 DEG C. Acid or alkaline agents may be used to accelerate the reaction. Suitable compounds include derivatives of fatty acids, such as caprylic, lauric, stearic, palmitic and montanic acids, and also oleic acid, ricinoleic acid or mixtures of these acids which are obtainable, for example, by the saponification of oils, fats or waxes or by the oxidation of high molecular weight non-aromatic hydrocarbons, such as paraffin waxes, paraffin oils, middle oils, and hydrogenation products of coals or tars; octyl, dodecyl, cetyl and oleyl alcohols, montanol, abietinol and similar alcohols, which can be obtained, for example, by catalytic reduction of the corresponding fatty acids or resin acids or their esters, as, for example, oils or fats; high molecular weight alcohols, which are obtainable by the oxidation of paraffin hydrocarbons or by condensation of low molecular weight alcohols or by adding on water to olefines, and also high molecular weight amines. Suitable compounds having aliphatic-aromatic radicles are, for example, octyl-phenol, dodecylphenol, octodecylaniline, and benzenes containing high molecular weight alkyl radicles. Carbon double linkages situated in conjugation to doubly-bound oxygen atoms, or vinyl groups or radicles containing or readily yielding such groups, may be introduced directly or through oxygen, nitrogen or sulphur atoms, as, for example, through hydroxyl, amino or mercapto groups, by etherification, esterification or amidation. Suitable compounds containing vinyl groups include vinyl ethers, vinyl esters, vinyl sulphides, vinyl sulphones, styrene derivatives, and vinylcarbazole derivatives. The introduction of such vinyl groups may be carried out by condensation of suitable compounds with vinyl compounds, for example vinyl alcohols, vinylamines or styrene and its derivatives, or also by splitting off water or hydrogen halides from suitable compounds. Styrene derivatives may be obtained, for example, by splitting off water from alkylated phenylethyl alcohols. The introduction of radicles having carbon double linkages in conjugated position to doubly-bound oxygen atoms, i.e. to carbonyl, carboxyl or sulphonyl groups, is effected, for example, by condensation of suitable compounds with maleic or fumaric acids, ethylidene-malonic acid or acrylic acid, or by condensation of mercaptans with acetylene and oxidation of the resulting vinyl compounds to the sulphones. The double linkage or vinyl group may be produced in situ from saturated organic compounds; for example, high molecular weight alcohols may be condensed with beta-halogencarboxylic acids, or high molecular weight carboxylic acids with halogen hydrins, unsaturated linkages being produced in the reaction products by splitting off hydrogen halide, or beta-amino-carbonyl or -carboxyl compounds, such as are obtainable by adding amines to unsaturated compounds containing carbonyl or carboxyl groups or by the reaction of beta-halogencarboxylic acid esters with amines, may also be used. Vinyl ketones may be obtained by splitting off water from ketone alcohols, by adding ethylene to acid chlorides and splitting off hydrogen chloride, or by the reaction of beta-halogen-propionic acid halides with Grignard compounds and subsequent splitting off of hydrogen halide. Compounds particularly specified are montanol acrylic acid ester, maleic acid di-octodecyl ester, hexadecyl vinyl ether, dodecyl vinyl sulphone, and hexadecyl vinyl ketone. They may be applied as dispersions or solutions in water or organic solvents such as benzine, carbon tetrachloride, trichlorethylene, ethyl alcohol, acetone or dioxane. Other waterproofing, emulsifying and wetting agents may be added. Examples describe the use of: (1) a solution in benzene and alcohol of maleic acid di-octodecyl ester made by heating maleic acid, octodecyl alcohol and bleaching earth under vacuum; (2) a solution in dioxane of dodecyl vinyl sulphone made by oxidizing dodecyl vinyl sulphide prepared from dodecyl mercaptan and acetylene; (3) an aqueous emulsion of maleic acid dioctodecyl ester containing ethylene glycol monocresyl ether, olein and triethanolamine, followed by treatment with acetic acid and heating; (4) an aqueous solution of b -(bromopyridinium)-propionic acid octodecyl ester, made by esterifying b -bromo-propionic acid with octodecyl alcohol and heating with pyridine, followed by heating in an atmosphere of ammonia, whereby the pyridinium compound is decomposed with formation of acrylic acid octodecyl ester; (6) a solution in tetrachlorethane of the compound <FORM:0498402/IV/1> where R is the alkyl radicle corresponding to the fatty acids of palm kernel oil, made by condensing maleic anhydride and stearylamine to form maleic acid monostearylamide which is converted by thionylchloride into the acid chloride which is then condensed with palm kernel oil alkyl-methylamine; (7) a benzene solution of heptadecyl vinyl ketone prepared by passing ethylene under pressure into a suspension of aluminium chloride in carbon disulphide containing stearic acid chloride, adding the reaction mixture to hydrochloric acid, removing the aqueous solution after standing, dissolving the residue in ether and washing till free from acid, adding acetone and evaporating; (8) a solution in alcohol and benzene of heptadecylchlorvinyl ketone made by passing acetylene into a solution of stearic acid chloride in carbon tetrachloride in the presence of aluminium chloride.