Iron-based amorphous metal and 6.5% silicon steel are competitive materials for high-power-density inductors in the low-to-medium-frequency range, and lead to a low cost and low,weight/volume solution for high-power dc-dc converters. In this paper, the practical effects of frequency, ripple, air-gap fringing, and thermal configuration are investigated for these materials. Inductor size can increase in both these laminated materials due to increased air-gap fringing core and copper losses. Distributing the air gap is demonstrated to reduce the inductor losses and size. It is also demonstrated that a thermal configuration ensuring beat flow in the direction of the material lamination results in optimum cooling. A 2.5 kW converter is built to verify the optimum material selection and thermal configuration over the ranges of frequency and ripple. Experimental, analytical and simulation results are presented.