A solid organic polymer is coated with an acid polysilicic acid ester (an ester of a polymeric silicic acid which ester contains OH groups attached to Si) solution. The coating is carried out by applying to the surfaces of the solid organic polymer the solution in a volatile organic solvent, allowing the solvent to evaporate, and baking at an elevated temperature, usually 75 to 100 DEG C. A very long list of organic polymers is given. The coating composition may also contain an organic solvent for the polymer being treated and organic polymer compatible with the polysilicic acid ester, e.g., polyvinyl butyral, urea-formaldehyde, phenol-formaldehyde, hydrolysed polyvinyl acetate or a hydrated ethylene/vinyl acetate copolymer and may also contain a carboxylic acid containing 2-5 carbon atoms per molecule, e.g., glacial acetic acid. Solvents specified are alcohols, e.g., butanol, ketones, esters of organic or inorganic acids, ethers, amides and acids. The acid polysilicic acid esters may vary in the ratio of silicic acid ester groups to Si atoms from 0.01 to 1 or less to 2 to 1 or more. The alcohol from which the acid polysilicic acid ester is derived may contain additional functional groups besides the hydroxyl, e.g., ether, mercaptan, halide, sulphide, ketone, ester, amide, nitro and nitrile groups. Specified alcohols are methyl, ethyl, n-butanol and tertiary butanol. The solution should preferably contain at least twenty per cent. of methyl, ethyl or butyl alcohol. The coated polymer may be subjected to a moist atmosphere containing an amino-compound (e.g., ammonia) or may be flushed with an aqueous amine solution. In examples (1) polymer films or sheets of (a) methyl methacrylate (b) vinyl chloride/acetate (c) vinyl chloride/diethyl fumarate (d) polyvinyl chloride (e) polyethylene (f) ethylene/vinyl acetate (g) polystyrene (h) polyvinyl butyral (i) polyvinyl alcohol plasticized with glycerol (j) Neoprene (k) fabric coated with unvulcanized rubber (1) rubber hydrochloride (m) hexamethylene diammonium sebacate-adipatecaprolactam interpolymer (n) N-methoxymethyl polyhexamethylene adipamide (o) Cellophane (p) ethyl cellulose (q) cellulose acetate or (r) nitrocellulose are coated with a butyl acid polysilicate solution in butanol containing polyvinyl butyral. Polymethyl methacrylate is coated with (2) and (6) n-butyl acid polysilicic acid (3) (4) tertiary butyl acid polysilicate (5) ethyl acid polysilicate (7) butyl polysilicate together with polyvinyl butyral (8) butyl polysilicate together with methacrylic acid (9) and (10) polyvinyl butyral modified butyl polysilicate (11) butyl polysilicate together with phenol-formaldehyde (12) diphenylolpropane - formaldehyde modified ethyl acid polysilicate; butyl polysilicate together with (13) both polyvinyl butyral and phenol-formaldehyde (14) polyethyl methacrylate (15) ethylene/vinyl acetate copolymer (16) melamine-formaldehyde (17) polyamide (18) a non-drying oil modified glyceryl phthalate resin (19) castor oil (20) hydroxy acetic acid modified castor oil (21) ethyl cellulose; and with (22) a polyvinyl acetate modified polysilicate. Specification 290,717, [Class 95], is referred to.ALSO:A solid organic polymer is coated with an acid polysilicic acid ester (an ester of a polymeric silicic acid, which ester contains OH groups attached to Si atoms) solution. The coating composition may contain an organic solvent such as alcohols (e.g. butanol) ketones, esters, of organic or inorganic acids, ethers, amides and acids. The alcohol from which the acid ester is derived may contain additional formational groups, e.g. ether, mercaptan, halide, sulphide, ketone, ester, amide, nitro and nitrile groups. Specified alcohols are methyl, ethyl, n-butanol and tertiary butanol. The preparation of the esters by acidifying an aqueous sodium silicate solution, esterifying and dehydrating, or by the controlled hydrolysis of ethylsilicate is mentioned. The following coating compositions are disclosed in the examples: (1) a butyl acid polysilicate solution in butanol containing polyvinyl butyral, (2) and (6) n-butyl polysilicic acid; (3) and (4) tertiary butyl acid polysilicate; (5) ethyl acid polysilicate; (7) butyl polysilicate together with polyvinyl butyral; (8) butyl polysilicate together with monomeric methacrylic acid (after coating the coated polymer is heated); (9) and (10) poly-vinyl butyral modified butyl polysilicate; (11) butyl polysilicate together with phenol-formaldehyde; (12) diphenylolpropane - formaldehyde modified ethyl acid polysilicate; butyl polysilicate together with (13) both polyvinyl butyral and phenol-formaldehyde; (14) polyethyl methacrylate; (15) ethylene/vinyl acetate; (16) melamine-formaldehyde; (17) polyamide; (18) a non-drying oil-modified glyceryl phthalate; (19) castor oil; (20) hydroxyacetic acid-modified c<\>aastor oil; (21) ethyl cellulose; and with (22) a polyvinylacetate-modified polysilicate. Specification 290,717, [Class 2 (iii)], is referred to.