Polyurethane-clay nanocomposite elastomers were synthesized using polyol-clay blends with different levels of dispersion, which affected the final elastomer microstructure. A PU-clay microcomposite elastomer containing partially dispersed clay showed poorer mechanical and similar fire properties to the unmodified polyurethane. More complete dispersion of the clay into the polyol led to an exfoliated structure in the final elastomer. This showed a higher modulus and kept a visco-elastic behavior to higher temperature than the pristine PU. The enhancement of mechanical and thermal properties in the nanocornposite elastomer can be attributed to the degree of clay exfoliation, and this also prevented dripping during the UL 94 fire test. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 2847-2853, 2009