A heat sink comprising an Al alloy open cell material within an insulated channel is described. It is attached to a silicon substrate and cooled with circulating air. The influence of foam morphology and heat sink dimensions on both the heat transfer coefficient and the pressure drop are measured. Trends in the cell wall diameter, d, the heat sink thickness, b, and the air velocity, v, are established. The findings are compared with a model based on the cross flow of a fluid over a bank of cylinders. There is qualitative consistency with the measured effects of d and v, but significant differences in details. Moreover, measured trends with b oppose those in the model. The implication is that the fluid flows are influenced by the heat sink thickness. Further studies are needed to assess these effects.