Magnetic Shielding Alloy Mu-Metal / HY-MU 80 Mumetal is 80% nickel with additions of iron and molybdenum as main elements in turn this alloy offers an extremely high initial permeability. It is only moderately resistant to moisture and atmospheric corrosion, it used mainly in in transformer cores but is well known for its magnetic properties which are used for shielding electrical components from magnetic fields. "HYMU 80" has a minimum DC permeability of 80,000 at a flux density of 40 gauss when heat treated by the recommended procedure and test in accordance with ASTM 596.