Montmorillonite clay was modified with an oligomeric surfactant, which was then melt blended with polyethylene and polypropylene in a Brabender mixer. The morphology was characterized by X-ray diffraction and transmission electron microscopy, while thermal stability was evaluated from thermogravimetric analysis and the fire properties by cone calorimetry. The nanocomposites are best described as mixed imn-scible/intercalated/delaminated systems and the reduction in peak heat release rate is about 40% at 5% inorganic clay loading. (c) 2005 Elsevier B.V. All rights reserved.