# High-permeability alloy (mu-metal) magnetic shielding

> The only material class that meaningfully attenuates power-frequency magnetic fields, and even then typically by a factor of two to five in a retrofit — which is why distance and source correction are preferred.

- Canonical URL: https://emfbase.com/shielding/high-permeability-alloy
- Collection: Shielding & remediation
- Record id: `shielding:shielding-mu-metal`
- Status: verified
- Last verified: 2026-08-12
- JSON: https://emfbase.com/api/shielding/high-permeability-alloy
- Also known as: mu metal, magnetic shielding, nickel iron alloy

## Key values

- **Form:** paneling
- **Targets:** elf magnetic
- **Grounding required:** No
- **Datasheet attenuation:** 3–14 dB — 50/60 Hz magnetic; roughly a factor of 1.5–5 in field strength for practical retrofits [niehs-emf]

## Failure modes

- Performance collapses if the sheet is bent, drilled or mechanically shocked after annealing
- Saturates in strong fields, at which point it stops shielding
- Only useful for compact, well-defined sources; useless against a whole-house net-current fault
- Cost per square metre is orders of magnitude above RF materials for a much smaller benefit

## Related records

- [High-voltage transmission line](https://emfbase.com/emitters/high-voltage-transmission-line): Fields directly beneath a loaded transmission line reach tens of milligauss and fall off roughly with distance for a balanced three-phase circuit, reaching background at 30–60 m for typical loadings.
- [Magnetic flux density](https://emfbase.com/quantities/magnetic-flux-density): The quantity an ELF gaussmeter reports, expressed in milligauss or microtesla, used to assess wiring, transformers and power lines. 1 µT = 10 mG.

## Sources

- `niehs-emf` National Institute of Environmental Health Sciences. *Electric and Magnetic Fields*. https://www.niehs.nih.gov/health/topics/agents/emf — government, link checked 2026-08-12
- `sbm-2024` Institut für Baubiologie + Nachhaltigkeit (IBN) (2024). *Building Biology Evaluation Guidelines for Sleeping Areas (SBM-2024)*. https://buildingbiology.com/site/downloads/SBM-2024_EVALUATION_GUIDELINES_EN.pdf — ngo, link checked 2026-08-12

Data licence: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Dataset version 2026.08.1. Retrieved from EMFBase, https://emfbase.com.

This record is reference data, not medical or legal advice. Regulatory limits, scientific guidelines and precautionary values are labelled separately and answer different questions.