Heat sensitive recording material

Heat sensitive recording material which contains in its colour reactant system a colour former, a developer for the colour former and also a sulphamide compound of the formula where R1, R2 and R3, independently of one another, are each hydrogen, unsubstituted or halogen-, hydroxy-, cyano- or lower alkoxy- substituted alkyl, cycloalkyl or unsubstituted or halogen-, cyano-, lower alkyl- or lower alkoxy- ring-substituted phenalkyl, phenyl or naphthyl or (R2 and R3) together with the nitrogen atom connecting them are a five- or six- membered, preferably saturated, heterocyclic radical where R1, R2 and R3 are not simultaneously hydrogen.