The most efficient magnetic shield shape is a spherical shield but this is difficult to manufacture in production terms. The next best is a cylinder with closed ends. The rounded surface of the cylinder is conductive to the absorption of magnetic flux. If the cylinder does not have end caps, the ratio of the length to the diameter should be 4:1.

     If space is at a premium, as well as being more practical for mechanical reasons, then a flat sided box fabricated from sheet metal will be the next best choice. The corners need to have a large bend radius to minimize flux leakage.

The least favorable shield shape is a flat Mu Metal strip because a flat strip only covers a portion of the flux path.

      It is necessary to ensure magnetic continuity whenever a shield is produced from a number of Mu Metal pieces, i.e. with lids, overlapping seams. Continuity can be achieved mechanically using friction or by welding.

     If the magnetic shield needs holes then the size of the holes should be chosen with care. As a rule magnetic fields can travel into any opening a distance of two times the hole diameter.

On large diameter holes, a branch tube can be employed to protect the hole from leakage.