Heat generating solids in the form of reactive multilayer sheets that alternate between two materials, each comprising one of the following element pairs, nickel and aluminium, aluminium and zirconium, aluminium and palladium, titanium and silicon, zirconium and silicon, niobium and silicon, titanium and carbon, zirconium and carbon, hafnium and carbon, titanium and boron, zirconium and boron, hafnium and boron, aluminium and copper oxide, aluminium and iron oxide, to be used for heat generation and which support self-propagating reactions and act as local heat sources in joining, ignition and propulsion applications