This standard gives the procedures to determine the thermal resistance of products the thicknessesof which exceed the maximum thickness for guarded hot plate or heat flow meter apparatus. Inany case most of the procedures described in this standard require apparatus that allows tests onspecimens up to 100 mm thick.This standard gives guidelines to assess the relevance of the thickness effect, i.e. to establishwhether the thermal resistance of a thick product can or cannot be calculated as the sum of thethermal resistances of slices cut from the product, these guidelines complement the indicationsgiven in ISO 8302:1991 on the guarded hot plate apparatus.This standard describes testing conditions which prevent the onset of convection. which couldtake place in some products under the considered temperature differences and thicknesses.