In general, magnetic field attenuation is a function of the permeability of the material. A better shielding material has high permeability per weight. For metallic foil and sheet, the most efficient shielding material is the 80 Nickel family (e.g., Molypermalloy), followed by the 50 Nickel alloys (e.g., Deltamax). The economical silicon-steel foils and sheets are also good shielding material when weight is not of a major issue.