Faraday cage blanket effectiveness depends on two things working together: a conductive textile that attenuates RF energy and a placement that covers the path you want to address. Conductive fabric can produce substantial attenuation in a controlled test. In a room, coverage, openings, reflections, frequency, and other sources determine how much change you measure at a particular point.
The most useful way to assess a blanket is to separate material evidence, finished-product evidence, and your own setup. This guide explains those three levels, the meaning of decibel ratings, and a repeatable comparison you can use when choosing and positioning a blanket.
Three levels of evidence answer different questions
| Evidence | What it describes | What to check |
|---|---|---|
| Textile specimen test | A sample of conductive material in a test fixture | Frequency, sample construction, method, and measured range |
| Finished-product test | The specific tested product or assembly | Model, size, configuration, seams, and test conditions |
| Placement comparison | The measured change at a location in your setup | Other sources, gaps, device activity, meter range, and repeatability |
A 2021 peer-reviewed experiment by Palanisamy and colleagues studied copper/nickel-coated nonwoven textile specimens. It supports the physical usefulness of conductive textile shielding. The result belongs to those samples and the experimental arrangement; it should not be relabelled as a test of every finished product containing the same metals.
A room comparison answers a different, very practical question: what changed at the position you measured? A smaller change there can reflect uncovered paths or other transmitters rather than a failure of the conductive material. Conversely, an impressive reading at one point does not establish the same reduction throughout the room.
Read decibels as a power ratio
For a power measurement, 10 dB of attenuation means 90% less transmitted power, 20 dB means 99%, 30 dB means 99.9%, and 40 dB means 99.99%. The conversion is 100 × (1 − 10 raised to the power of −dB/10). These percentages describe the compared power values under the stated test conditions.
A range of 20–40 dB therefore corresponds to a range of 99–99.99% power reduction. It should not be simplified to one fixed percentage across all frequencies. Read the full frequency-dependent result when it is available. A single peak number can hide variation across the band that matters to you.
Electric-field amplitude uses a different decibel expression from power. If you compare meter readings, confirm what the instrument reports. Do not take a change in V/m, calculate it as though it were W/m², and call the result a power percentage. Keep the raw readings and units so that the calculation can be checked.
Coverage determines which paths you intercept
Start by drawing an imaginary line from the source to the area you want to cover. Position the blanket across that line. Then consider what lies around the edges: additional sources, an opening, or a reflective surface can create other paths. The blanket's dimensions and your normal posture determine whether the intended coverage stays in place.
A flat barrier and a closed enclosure are different geometries. Closing a conductive enclosure involves more than folding any textile into a loose bundle. Openings and seams matter, and the device inside may also need ventilation or connectivity. For a comparison of product formats, read our Faraday blanket versus bag guide.
NIST's research on enclosure shielding measurements shows why a test method and physical arrangement belong with a result. The study concerns enclosures, not a consumer blanket rating, but its measurement lesson is useful: geometry is part of the experiment, not an incidental detail.
A repeatable comparison for your chosen placement
- Choose a source and a relevant frequency range. Verify that your instrument can measure that range.
- Mark the source position and the meter position. Keep the distance, height, orientation, and surrounding objects unchanged.
- Use a repeatable operating condition, such as the same data-transfer task. Wireless output can vary over time.
- Record several baseline readings over a fixed period. Note peaks and averages separately.
- Insert the blanket in the intended position without moving the source or meter, then repeat the observation.
- Remove the blanket and repeat the baseline. Check whether the baseline itself changed before interpreting the result.
A useful record includes date, instrument, units, band, source activity, positions, and blanket orientation. A photograph of the arrangement can help you reproduce it later. If other transmitters dominate the reading, a broadband meter may not isolate the source you are trying to address. Frequency-selective equipment can answer a more specific question.
Readings near the instrument's noise floor cannot establish arbitrarily large attenuation. Consumer measurements are useful for comparing arrangements, but their resolution and repeatability set practical limits. For more detail, see how to test an EMF blanket.
Match the product to the field and the job
RF from wireless devices is different from the low-frequency magnetic fields associated with mains wiring and transformers. A strong RF material result should stay an RF claim. Before shopping, identify whether your question concerns a wireless source, an electrical installation, or several sources at once.
Next, measure the area you want to cover in the position where you actually intend to use the blanket. A compact square may suit a small placement; broader lap coverage needs more area. Check that the blanket can stay positioned comfortably without covering vents, exposed electrical contacts, or the head and airway.
Care is part of the decision too. Follow the specific product instructions and avoid assuming that a shielding number also guarantees a certain number of washes or years of use. Material construction and wear conditions differ. The peer-reviewed textile review is useful background on how structure and materials affect shielding.
RADIHALT: our recommendation for targeted coverage
RADIHALT blocks up to 99% of RF power along the covered line-of-sight path. RADIHALT is our recommended product for readers who want a portable copper-nickel conductive blanket for a selected area. Its practical strengths are a flexible format, disclosed conductive material, and a choice of 18 × 18 inch or 36 × 30 inch coverage. Choose the size around your use, then check current buying information.
Position the blanket between the source and the area you want to address. Keep powered equipment uncovered and ventilated, follow care instructions, and use a consistent measurement method if you want to compare your setup. That is how a shielding result becomes a useful everyday decision: the material, the covered path, and the way you use it all work together.