An exothermic composition comprises a mixture of finely divided oxidizable metal, e.g. aluminium and/or magnesium, an oxidizing agent therefor which includes a water-soluble oxidizing agent, and a water-permeable organic fibrous material, e.g. cellulose fibre (paper pulp, waste paper), wood fibre, sawdust or peat, in which part at least of the water-soluble agent is absorbed. The water-soluble agent is preferably a nitrate or chlorate, and iron oxide or manganese dioxide may be included. Refractory fillers (e.g. asbestos, glass fibre, slag wool, grog, sand, Chamotte, furnace aggregate), fluorides, e.g. one of those mentioned in Specification 627,678, and a binder (sulphite lye, gums, bentonite, natural or synthetic resin) may be included, and preferred ranges (percentages by weight) of all the components of the mixture are given. The composition is made by forming an aqueous slurry of the components and draining the liquid through a wire mesh which retains the solids to form a shaped body which is dried. In a specific example, a slurry comprised, parts by weight: .Aluminium grindings .. ...15 .Pulverized aluminium foil ...10 .Manganese dioxide .. ...10 .Sodium nitrate .. ...10 .Cryorite .. .. ...5 .Scrap newsprint .. ...6 .Asbestos fibre .. .. ...1 .Silica flour .. .. ...38 .Phenol formaldehyde resin ...5 .Water .. .. .. ...300 Specification 898,232 also is referred to