What materials can I use to block/shield magnetic fields?

Magnetic fields cannot be blocked, only redirected. The only materials that will redirect magnetic fields are materials that are ferromagnetic (attracted to magnets), such as iron, steel (which contains iron), cobalt, and nickel. The degree of redirection is proportional to the permeability of the material. The most efficient shielding material is the 80 Nickel family, followed by the 50 Nickel family.

What materials do magnets attract?

Ferromagnetic materials are strongly attracted by a magnetic force.  The elements iron (Fe), nickel (Ni), and cobalt (Co) are the most commonly available elements. Steel is ferromagnetic because it is an alloy of iron and other metals.

What is the difference between the maximum operating temperature and the Curie temperature of the magnets?

The maximum operating temperature is the maximum temperature the magnet may be continuously subjected to with no significant loss of magnetic strength. This is 176ºF (80ºC) for standard grades of neodymium magnets. The Curie Temperature is the temperature at which the magnet will become completely demagnetized. This is 590ºF (310ºC) for standard grades of neodymium magnets. Higher temperature grades have higher maximum operating temperatures and higher Curie Temperatures. At temperatures between these two points, a magnet will permanently lose a portion of its magnetic strength. The loss will be greater the closer to the Curie Temperature it is heated.

Are there any regulations for shipping magnets?

According to the United States Department of Transportation and the Office of Hazardous Materials Safety, the limit for shipping magnets by air is a magnetic field strength of 0.00525 Gauss measured at 15 feet (4.5 meters) from any point on the outside of the package. There are no restrictions on the shipping of magnetized materials by ground. When in doubt, ship magnets by ground transportation.