Multi-wall carbon nanotubes (CNT) were coated with protonated polyaniline (PANI) in situ during the polymerization of aniline. The content of CNT in the samples was 0-80 wt%. Uniform coating of CNT with PANI was observed with both scanning and transmission electron microscopy. An improvement in the thermal stability of the PANI in the composites was found by thermogravimetric analysis. FTIR and Raman spectra illustrate the presence of PANI in the composites; no interaction between PANI and CNT could be proved. The conductivity of PANI-coated CNT has been compared with the conductivity of the corresponding mixtures of PANI and CNT. At high CNT contents, it is not important if the PANI coating is protonated or not; the conductivity is similar in both cases, and it is determined by the CNT. Polyaniline reduces the contact resistance between the individual nanotubes. A maximum conductivity of 25.4 S cm(-1) has been found with PANI-coated CNT containing 70 wt% CNT. The wettabitity measurements show that CNT coated with protonated PANI are hydrophilic, the water contact angle being similar to 40 degrees, even at 60 wt% CNT in the composite. The specific surface area, determined by nitrogen adsorption, ranges from 20 m(2) g(-1) for protonated PANI to 56 in for neat CNT. The pore sizes and volumes have been determined by mercury porosimetry. The density measurements indicate that the compressed PANI-coated CNT are more compact compared with compressed mixtures of PANI and CNT. The relaxation and the growth of dimensions of the samples after the release of compression have been noted. (c) 2006 Elsevier Ltd. All rights reserved.