On the basis of two examples, temperature measurements are proposed within burning polymer specimen during the cone calorimeter test; especially to gain deeper insight into the actual pyrolysis conditions and flame retardancy mechanism. The heating and pyrolysis within a poly(methyl methacrylate) specimen were characterized, discussing the characteristic maximum heating rates (165−90°Cmin−1 decreasing with depth within the specimen and >275°Cmin−1 at the initial surface), pyrolysis temperature (454−432°C decreasing in accordance with decreasing heating rates), thickness of the pyrolysis zone (0.5–1.3 mm) and its velocity (1.2−2.1 mm min−1) as a function of sample depth and burning time. Thermally thick behaviour corresponds to a pyrolysis zone thickness of 0.74 mm and a velocity of 1.51 mm min−1 and occurs until the remaining specimen thickness is less than 8 mm. The shielding effect against radiation occurring in a layered silicate epoxy resin nanocomposite was investigated. It is the main flame retardancy effect of the silicate-carbon surface layer formed under fire. The reradiation from the hot surface is increased by a factor of around 4–5 when an irradiance of 70kWm−2 is applied. The energy impact into the pyrolysis zone is crucially reduced, resulting in a reduction of fuel production and thus heat release rate. Copyright © 2009 John Wiley & Sons, Ltd.