Carbon foams with improved thermal conductivity and mechanical properties were prepared from a tannin-based resin and exfoliated graphite used as filler. Organic foams were first prepared by suspending exfoliated graphite in an aqueous solution of tannin, furfuryl alcohol, formaldehyde, diethyl ether and para-toluene-4-sulphonic acid at room temperature. Spontaneous foaming started after a short induction time, and the resultant dark brown, hard, foams were carbonized at 1173 K. The addition of exfoliated graphite in the foam matrix increased the thermal conductivity by more than one order of magnitude, passing from 0.11 W m(-1) K-1 for pure tannin-based carbon foams to 3.65 W m(-1) K-1 for composite foams. In the same time, compressive strength and elastic modulus increased from 3.6 to 6.9 MPa and from 30.1 to 61 MPa, respectively. Such biomass-derived carbon foams are suitable porous structures for hosting phase change materials for seasonal storage applications. (C) 2014 Elsevier Ltd. All rights reserved.