The thermal and hydraulic characteristics of forced-convective transfers from arrays of vertical, uniformly spaced, rectangular fins, aligned parallel to an undisturbed air stream, have been investigated experimentally. For a constant temperature of the fins' base, at each air flow rate and shroud clearance gap to fin-height ratio, optimal inter-fin separations, corresponding to the maximum steady-state rate of heat transfer, have been determined. The thermal conductivity of the material of the fins had only a relatively small effect on the rate of heat transfer through the array of fins. So optimal geometrical configurations of even relatively low thermal-conductivity plastic material could be usefully employed as covers for rapidly heat-dissipating enclosures for electronic systems.