Cellular cured polymeric material, e.g. of rubber or of urea, phenol, or melamine aldehyde resin, or of a vinyl polymer is prepared by incorporating into a mix of the uncured material as a blowing agent an organic N-substituted sulphonyltriazene, and heating to expand and cure the mix. The N-substituted sulphonyltriazene may have the formula <FORM:0783745/IV (a)/1> in which R is a cycloalkyl, aralkyl, aryl or heterocyclic radical, R1 is an aryl or heterocyclic radical, and R2 is an aliphatic radical linked through a saturated carbon atom to the nitrogen, or the formula <FORM:0783745/IV (a)/2> in which R is a mono- or di-arylene radical in which the nuclei of the diarylene radical may be interposed by an oxygen or sulphur atom, R1 is an aromatic or heterocyclic radical, and R2 is an aliphatic radical linked through a saturated carbon atom to the nitrogen, or the formula <FORM:0783745/IV (a)/3> in which R is a cycloalkyl, aralkyl, aryl, or heterocyclic radical, R1 is a diarylene radical in which the nuclei may be interposed by an oxygen or sulphur atom, and R2 is an aliphatic radical linked through a saturated carbon atom to the nitrogen. Several compounds of the above formul are specified. In Example 3 a cellular material was prepared by heating at 153 DEG C. for 40 minutes and 500 p.s.i., and at 100 DEG C. for 60 minutes, a mixture of 100 parts (by weight) of a vinyl resin, 130 parts dioctyl phthalate, a heat stabilizer (4 pts.) and 10 parts of 1 - benzenesulphonyl - 3 - methyl - 3 - phenyltriazene. Other triazene blowing agents are specified.ALSO:An N-substituted sulphonyltriazene for use as a blowing agent in preparing cellular cured polymeric material (see Group V) may have the formula <FORM:0783745/IV (a)/1> in which R is a cycloalkyl, aralkyl, aryl or heterocyclic radical, R1 is an aryl or heterocyclic radical, and R2 is an aliphatic radical linked through a saturated carbon atom to the nitrogen, or the formula <FORM:0783745/IV (a)/2> in which R is a mono- or diarylene radical in which the nuclei of the diarylene radical may be interposed by an oxygen or sulphur atom, R1 is an aromatic or heterocyclic radical, and R2 is an aliphatic radical linked through a saturated carbon atom to the nitrogen, or the formula <FORM:0783745/IV (a)/3> in which R is a cycloalkyl, aralkyl, aryl, or heterocyclic radical, R1 is a diarylene radical in which the nuclei may be interposed by an oxygen or sulphur atom, and R2 is an aliphatic radical linked through a saturated carbon atom to the nitrogen. The N-substituted sulphonyltriazene may be prepared by treatment of a monosulphonamide, e.g. cyclohexane sulphonamide, with a diazonium salt, e.g. benzene diazonium chloride, to obtain a diazosulphonamide. The latter is then treated with, for example, dimethyl or diethyl sulphate or with acrylonitrile to obtain the aliphatic radical R2. Alternatively a bis-sulphonamide, e.g. pxylene disulphonamide, or a tetrazo compound, e.g. a salt of 4,41-diamino-diphenyl ether, may be analogously rested to form bis-sulphonyltriazenes. Lists of starting materials given include compounds substituted with alkyl, alkoxy, acetoxy, acidylamino, chlorine, cyano and nitro radicals. Specified products are 1-benzenesulphonyl-3-methyl-3-phenyltriazene, 1-benzenesulphonyl - 3 - methyl - 3 - para - tolyltriazene, 1 - benzenesulphonyl - 3 - methyl - 3 - ortho-tolyltriazene, 1 - benzenesulphonyl - 3 - methyl-3 - para - anisyltriazene, 1 - benzenesulphonyl-3 - methyl - 3 - para - chlorophenyltriazene, 1 - benzenesulphonyl - 3 - methyl - 3 - meta-chlorophenyltriazene, 1 - benzenesulphonyl - 3 - ethyl - 3 - para - tolyltriazene, 1 - benzenesulphonyl - 3 - cyanoethyl - 3 - phenyltriazene, 1 - benzenesulphonyl - 3 - cyanoethyl - 3 - para-chlorophenyltriazene, 1 - benzenesulphonyl - 3 - cyanoethyl - 3 - para - tolyltriazene, 1 - phenylmethanesulphonyl - 3 - methyl - 3 - meta-tolyltriazene, 1 - benzylsulphonyl - 3 - methyl-3 - phenyltriazene, 1 - (para - toluenesulphonyl)-3 - methyl - 3 - phenyltriazene, 1 - (para-toluenesulphonyl) - 3 - methyl - 3 - para - tolyltriazene, 1 - (para - toluenesulphonyl) - 3 - cyanoethyl - 3 - phenyltriazene, 1 - (para) - methoxybenzenesulphonyl) - 3 - ethyl - 3 - (para-methylphenyl) - triazene, 1 - (para - methoxybenzenesulphonyl) - 3 - methyl - 3 - phenyltriazene, 1 - (ortho - chlorobenzenesulphonyl)-3 - cyanoethyl - 3 - phenyltriazene, 1 - (para-chlorobenzenesulphonyl) - 3 - methyl - 3 - phenyltriazene, 1 - (5 - acetamido - 2 - thiadiazolesulphonyl) - 3 - methyl - 3 - para - tolyltriazene, 1 - (5 - quinolinesulphonyl) - 3 - cyanoethyl - 3 - para - anisyltriazene, 3:31 - (4:41-biphenyl) - bis - (3 - methyl - 1 - benzenesulphonyltriazene) and 1:11 - (1:5 - naphtholenedisulphonyl) - bis - (3 - methyl - 3 - phenyltriazine. The above triazenes are numbered: <FORM:0783745/IV (a)/4>ALSO:Cellular cured, polymeric material, e.g. of rubber or of urea, phenol, or melamine aldehyde resin, or of a vinyl polymer is prepared by incorporating into a mix of the uncured material as a blowing agent an organic N-substituted sulphonyltriazine, and heating to expand and cure the mix. The N-substituted sulphonyltriazene may have the formula: <FORM:0783745/V/1> in which R is a cycloalkyl, aralkyl, aryl or heterocyclic radical, R1 is an aryl or heterocyclic radical, and R2 is an aliphatic radical linked through a saturated carbon atom to the nitrogen, or the formula: <FORM:0783745/V/2> in which R is a mono- or diarylene radical in which the nuclei of the diarylene radical may be interposed by an oxygen or sulphur atom, R1 is an aromatic or heterocyclic radical and R2 is an aliphatic radical linked through a saturated carbon atom to the nitrogen, or the formula: <FORM:0783745/V/3> in which R is a cycloalkyl, aralkyl, aryl, or heterocyclic radical, R1 is a diarylene radical in which the nuclei may be interposed by an oxygen or sulphur atom, and R2 is an aliphatic radical linked through a saturated carbon atom to the nitrogen. The N-substituted sulphonyltriazene may be prepared by treatment of a monosulphonamide, e.g. cyclohexane sulphonamide, with a diazonium salt, e.g. benzene diazonium chloride, to obtain a diazosulphonamide. The latter is then treated with, for example, dimethyl or diethyl sulphate or with acrylonitrile to obtain the aliphatic radical R2. Alternatively a bis-sulphonamide, e.g. p-xylene disulphonamide, or a tetrazo compound, e.g. a salt of 4, 41 diamino-diphenyl ether, may be treated with the diazonium salt. Several compounds of the above formulae are specified. In one Example samples of cellular material are prepared by heating at 153 DEG C. for 35 minutes, and at 130 DEG C. for 60 minutes, mixes comprising 100 parts by weight of plasticized rubber, vulcanizing and other ingredients, and 1,5 parts of a blowing agent. Various samples are prepared using several different blowing agents including 1-benzenesulphonyl-3-methyl-3-phenyl-triazene, 3, 31-(4, 41 biphenyl)-bis-[3 methyl-1-benzene-sulphonyltriazene], 1, 11 (1, 51 naphthalene disulphonyl)-bis-[3-methyl-3 phenyl-triazene].