The thermal response of aluminium matrix composites containing high volume fractions of SiC particulate has been investigated. The composites were produced by infiltrating aluminium into preforms made either from a single particle size, or by mixing and packing SiC particulate of two largely different average diameters. The results indicate that the hysteresis in the thermal strain response curves is proportional to the square root of the particle surface area per unit volume of metal matrix, in agreement with current theories. The difficulties in applying the same approach to composites with bimodal size distributions are discussed. On the other hand, the overall Coefficient of Thermal Expansion (CTE) is shown to be mainly determined by the composite compactness or total particle volume fraction; neither the particle average size nor the particle size distribution, affect the overall CTE. This result is in agreement with previously published numerical results.