A large number of studies using the cone calorimeter showed that nanoparticles used even in small quantities (e.g. 3 wt.%) improve fire retardancy by reducing significantly the heat release rate/mass loss rate. The improved fire retardancy by nanocomposites has been attributed usually to the formation of a surface layer as a result of accumulation of nanoparticles on top of the virgin polymer because this surface layer not only acts as mass and thermal barriers to the polymer underneath but primarily increases surface radiation losses as the surface temperature increases. Various theories have been proposed for qualitatively explaining the mechanism of nanoparticles action, including mainly (a) gasification of polymer and precipitation of nanoparticles, (b) migration of nanoparticles towards the surface and (c) nanoconfinement. However, quantitative investigation on the effects of nanoparticles on pyrolysis has never been undertaken. In this work, square samples of a polyamide 6 (PA6) nanocomposite were tested in the cone calorimeter under different heat fluxes. By combining the experimental mass loss data and numerical calculations, a novel approach is developed to quantify the effects of nanoparticles and subsequently to predict pyrolysis of the PA6 nanocomposite at different heat fluxes and thicknesses, in good agreement with the experimental data. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.