Copper matrix composites reinforced with low thermal expansion ceramic particles, i.e. SiO2, AIN and diamond, in the range of ceramic volume fractions between 0.55 and 0.85 have been prepared by gas pressure infiltration and are characterized by their coefficient of thermal expansion (CTE). It is shown that the composite CTE is strongly affected by the ratio between the stiffness of the matrix and that of the particles. For the Cu/SiO2 composites, the CTE is above the rule of mixture in agreement with elastic theory. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.