Relative permeability is the permeability of the material divided by the permeability of free space . The permeability of most materials is very close to 1 .
For example 4 % Si steel has an initial relative permeability ( at or near 0T ) of 2,000 and a maximum permeability of 35,000 and indeed the relative permeability of any material at a sufficiently high field strength is 1 .