This paper discusses the potential for developing substantive intumescent, flame retardant fibres. It also reviews very recent work in the authors' laboratories that has demonstrated the successful reaction of char-promoting polyol phosphoryl chlorides with fibres containing active hydrogens such as cellulose flame retarded cellulose, wool and polyamide. Results show that satisfactory char enhancement occurs with evidence that intumescent character exists in some of these and that the chemical treatments are resistant to boiling in water. Using this chemistry, there is the potential, therefore, of creating the first generation of substantive intumescent fibres that will provide a cost-effective range of textiles with significantly enhanced fire resistant properties. (C) 2003 Kluwer Academic Publishers.