The d.c. conductivity a of zeolite/polyani line (PANI) and zeolite/polypyrrole (PPy) blends of various concentrations in zeolite was measured from 80 to 320 K. Moreover, the thermal degradation of sigma was studied by heating the blends at 70 degrees C under environmental conditions for times between 0 and 600 h approximately. The experimental results indicate a structure of the granular metal type, in which conductive grains are randomly distributed in an insulating matrix and thermal degradation is due to the shrinking of them. As the zeolite content increases in the zeolite/ppy blends, the separation between the conductive grains decreases, the conductivity increases and the thermal stability of the blends improves. On the contrary, the behaviour of the zeolite/PANI samples is almost independent from the zeolite content. An explanation of this difference is proposed based on the crystalline character of the conductive grains in PANI in contrast to the amorphous grains of PPy. (C) 2006 Elsevier B.V. All rights reserved.