Rubber-like materials are prepared by causing a thioaldehyde or polymer thereof, or a mixture of thioaldehyde or polymer thereof with an aldehyde or polymer thereof to react with sulphur at a temperature between 50 DEG and 200 DEG C. in the presence of a substance which imparts to the reaction medium a pH value between 1.5 and 10, e.g. borax, trisodium phosphate, potassium dihydrogen phosphate, or zinc oxide. Suitable thioaldehyde starting material is the product of the action of hydrogen sulphide on an aldehyde, e.g. formaldehyde, acetaldehyde or benzaldehyde. Magnesium oxide may be present to inhibit the agglomeration of the rubber-like reaction product and yield a latex-like composition. The products are generally elastic and insoluble in mineral oils and the usual rubber solvents except carbon disulphide. They may be compounded or vulcanized. Their harness varies with the proportion of sulphur and increases with the pH of the medium. They may be converted into secondary products which are elastic and of great strength and toughness by treatment with an acid-condensing agent such as sulphuric acid or aluminium chloride. These secondary products are resistant to acids such as strong mineral acids and even nitric or chromic acid. They may be compounded and vulcanized alone or with the primary products of the invention; natural or synthetic rubber, factice, sulphur, or natural or artificial resins. Filling materials may be added at any stage in the manufacture. Accelerators may be added at the compounding stage. Examples describe: (1) reaction of hydrogen sulphide with formaldehyde solution neutralised with borax to form the starting material which is refluxed with sulphur in presence of borax; (2) treatment of the product of example (1) with sulphuric acid; (3) as in (1), the treatment with sulphur being conducted in presence of trisodium phosphate or potassium dihydrogen phosphate or under substantially neutral conditions without the addition of a phosphate; (4) as in (1), the treatment with sulphur being performed in the presence of zinc oxide and the product being emulsified in aqueous medium to form a latex; (5) reaction between hydrogen sulphide and acetaldehyde in presence of trisodium phosphate and treatment of the reaction product with sulphur in presence of zinc oxide; (6) reaction of hydrogen sulphide on a mixture containing benzaldehyde, sulphur, ethyl alcohol and sulphuric acid; (7) treatment of the thioformaldehyde product of example (3) with sulphur, disodium phosphate and white factice; (8) treatment of the thioformaldehyde product of example (3) with sulphur, zinc oxide and magnesium oxide to yield a latex; (9) the product of examples (1), (2), (3), (5) or (7) is compounded with diphenyl guanidine, dibenzthiazole-1 : 11-disulphide, stearic acid, carbon and zinc oxide. The mixing rollers may be slightly heated. The products are obtained as sheets, the degree of vulcanization of which depends on the temperature of mixing; (10) the sheets of example (9) may be moulded and are fully vulcanized in an open steam oven; (11) the sheets of example (9) are rolled very thin and calendered on to textile material, vulcanization taking place during the calendering; (12) sheets of example (9) are vulcanized by wrapping them in cotton cloth and immersing in heated water; (13) as in example (9), with the further addition of sulphur powder and subsequent vulcanization; (14) one of the products of example (3) is compounded with diphenyl guanidine, dibenzthiazole-1 : 11-disulphide, smoked sheets, stearic acid, carbon and zinc oxide. The thin sheets are wound round glass tubing, wrapped with cotton, vulcanized as in example (10), and the formed rubber tubes unwrapped from the cotton covering.ALSO:Rubber-like materials are prepared by causing a thioaldehyde or polymer thereof, or a mixture of thioaldehyde or polymer thereof with an aldehyde or polymer thereof to react with sulphur at a temperature between 50 and 200 DEG C. in the presence of a substance which imparts to the reaction medium a pH value between 1.5 and 10. Suitable substance for imparting the desired pH value to the reaction medium are borax, trisodium phosphate, potassium dihydrogen phosphate, or zinc oxide. Suitable thioaldehyde starting material is the product of the action of hydrogen sulphide on an aldehyde, e.g. formaldehyde, acetaldehyde or benzaldehyde. Magnesium oxide may be present to inhibit the agglomeration of the rubber-like reaction product and yield a latex-like composition. The products are generally elastic and insoluble in mineral oils and the usual rubber solvents except carbon disulphide. They may be compounded and vulcanised. Their hardness varies with the proportion of sulphur and increases with the pH of the medium. They may be converted into secondary products which are elastic and of great strength and toughness by treatment with an acid condensing agent such as sulphuric acid or aluminium chloride. These secondary products are resistant to acids such as strong mineral acids and even nitric or chromic acid. They may be compounded and vulcanised alone or with the primary products of the invention; natural or synthetic rubber, fastice, sulphur or natural or artificial resins. Filling materials may be added at any stage in the manufacture. Accelerators may be added at the compounding stage. Examples describe: (1) Reaction of hydrogen sulphide with formaldehyde solution neutralised with borax to form the starting material which is refluxed with sulphur in presence of borax. (2) Treatment of the product of Example 1 with sulphuric acid. (3) As in (1) the treatment with sulphur being conducted in presence of trisodium phosphate or potassium dihydrogen phosphate or under substantially neutral conditions without the addition of a phosphate. (4) As in (1) the treatment with sulphur being performed in the presence of zinc oxide and the product being emulsified in aqueous medium to form a latex. (5) Reaction between hydrogen sulphide and acetaldehyde in presence of trisodium phosphate and treatment of the reaction product with sulphur in presence of zinc oxide. (6) Reaction of hydrogen sulphide on a mixture containing benzaldehyde, sulphur, ethyl alcohol and sulphuric acid. (7) Treatment of the thioformaldehyde product of Example 3 with sulphur, disodium phosphate and white factice. (8) Treatment of the thioformaldehyde product of Example 3 with sulphur, zinc oxide and magnesium oxide to yield a latex. (9) The product of Examples 1, 2, 3, 5 or 7 is compounded with diphenyl guanidine, dibenzthiazole-1 : 11-disulphide, stearic acid, carbon and zinc oxide. The mixing rolls may be slightly heated. The products are obtained as sheets the degree of vulcanisation of which depends on the temperature of mixing. (10 The sheets of Example 9 may be moulded and are fully vulcanised in an open steam can (11). The sheets of Example 9 are rolled very thin and calendered on to textile material, vulcanisation taking place during the calendering. (12) Sheets of Example 9 are vulcanised by wrapping them in cotton cloth and immersing in heated water. (13) As in Example 9 with the further addition of sulphur powder and subsequent vulcanisation. (14) One of the products of Example 3 are compounded with diphenyl guanidine dibenzthiazole-1 : 11-disulphide, smoked sheets, stearic acid, carbon, and zinc oxide. The thin sheets are wound round glass tubing, wrapped with cotton, vulcanised as in Example 10, and the formed rubber tubes unwrapped from the cotton covering.