Abstract: A cellular intumescent material comprising a substantially open-called substrate impregnated with a flexible intumescent polymer. The open-celled nature of the substrate is retained. The substrate may be a latex or urethane-based foam, a natural rubber or a synthetic rubber. The impregnant comprises at least a binder (A) and an intumescent component (B).The binder (A) can be a polyester, a liquid polymer system, a resin, a latex or an elastomer solution.The intumescent component (B) consists of a carbonific element (e.g. starch, sugar, sorbitol or pentaerythritol, or a compound which can polymerize to a "ladder" structure) and a spumific element (e.g. an inorganic acid or a precursor therefor).On exposure to a flame the materials flame initially but form a protective char and subsequently extinguish. The char prevents further burning of the treated material.