This nickel-iron alloy has a very high magnetic permeability, which is a measure of a material's ability to become magnetised when exposed to a magnetic field. No known material can stop magnetic field lines, but the high permeability of this alloy allows it to redirect (and thus control or limit) magnetic fields.
It is used for shielding sensitive electronic components in PCs, cell phones, hi-fi equipment, electric power transformers, and electron microscopes.
The shielding effect is high for low-strength and low-frequency magnetic fields. Stronger magnetic fields cause a magnetic saturation of the metal, which cause it to lose its effectiveness. In such cases, steel provides better shielding. The permeability is affected by the strength and frequency of the magnetic field, along with humidity and temperature. The permeability can be reduced when the material is shaped, but the properties can be recovered by heating to temperatures above 400ºC (aka annealing). The product is also known under the name MuMetal.
You can get a 20 cm x 20 cm sheet or a 6,5 cm x 6,5 cm sheet.
PS. We will send you a PDF of the datasheet for the material. We will CC the supplier when sending the mail, so you have the contact details if you need more information or support.