What Materials Can I Use to Block or Shield Magnetic Fields?
No material makes a magnetic field disappear, but ferromagnetic metals redirect it. A steel plate or cup gives field lines an easy path, so they travel through the steel instead of the space behind it. Mu-metal works better for weak fields around sensitive electronics. Aluminum, copper and brass don’t shield a magnet’s static field.
Shielding Materials Compared
| Material | Shields a magnet’s field? | Best for |
|---|---|---|
| Low-carbon steel | Yes | Strong neodymium magnets; cheap and easy to find |
| Mu-metal (nickel-iron alloy) | Yes, Very Well | Weak fields near electronics; saturates with strong magnets |
| 400-series stainless steel | Some | Where corrosion resistance matters |
| 300-series stainless steel | Little or None | Not a good shield |
| Aluminum, copper, brass | No | Only affects changing fields (eddy currents) |
| Plastic, wood, glass | No | Only adds distance |
How Thick Should a Steel Shield Be?
Steel can only carry so much magnetic flux. If it’s too thin for the magnet, it saturates and the extra field leaks through to the other side. Strong magnets need thicker steel, and sometimes two layers with an air gap between them. The right thickness depends on the magnet’s size and what you’re protecting, so test with your real parts: hold a phone compass or a paper clip on the far side and see how much field gets through.
Distance Is the Simplest Shield
A magnet’s field falls off quickly with distance. Moving a magnet a few inches away from a sensor, card or screen often solves the problem without any shield.
Ready-Made One-Sided Magnets
Pot Magnets, Channel Magnets and Threaded Pot Magnets already use a steel cup or channel to concentrate the field on one face and keep the back weak.