The use of nanocomposites in textile applications, and in particular of polyurethane (PU) coatings reinforced by various additives [clay and polyhedral oligomeric silsesquioxane (POSS)], has grown in recent years. Some interesting results have been obtained, especially with Cloisite 30B (a montmorillonite organo-modified by an alkyl ammonium cation bearing two primary hydroxyl functions): the thermal behavior and the reaction to fire were improved, but the structure (microcomposite, exfoliated, intercalated) was not really determined. This study focuses on polyurethane coatings reinforced with Cloisite 30B. The interactions between the diisocyanate and the counterions of Cloisite 30B and the structure obtained were demonstrated and discussed. (C) 2004 Wiley Periodicals, Inc.