Mumetal is one of a family of three Nickel-Iron alloys widely used to produce magnetic parts and shielding.

The three alloys concerned have the following approximate compositions and well known trade names:-

36%NiFe widely known as Supra 36, Nilomag36, Radiometal 36, Magnifer36
50%NiFe widely known as Supra 50, Nilomag 50, Radiometal 50, Magnifer 50
80%NiFe 5%Mo widely known as Mumetal, Magnifer

For shielding applications it is possible to use a combination of 2 or more layers of these alloys to arrive at the correct level of shielding without the shield becoming saturated.

For example; A combination of mu metal and a 50%NiFe is frequently used.

The 50% material has a much higher saturation level and can reduce the effect of any magnetic field substantially, leaving a second layer of mu-metal to further reduce the effect on the shielded item because of its much higher permeability without becoming saturated. This is due to the fact that the 50% material has already reduced the magnetic field considerably before it reaches the mumetal layer.

Relative properties of these three materials are shown below:-

                            Max Permeability                Saturation Flux Density(Tesla)

Mumetal                   400000                                                0.76

50% NIFe                  100000                                                 1.60

36%NiFe*                   25000                                                  1.30

*36% material is used mainly for low cost shieldings