Why Material Matters

Electromagnetic shielding works because conductive materials reflect and absorb RF energy. But “conductive” is a spectrum, not a binary. Different materials conduct electricity differently, which means they interact with electromagnetic waves differently. The material you choose for shielding determines how much energy is blocked, at which frequencies, for how long, and at what cost.

Dispatch #003 explored the tin-versus-aluminum distinction — the material switch that changed what “tinfoil” means. This dispatch expands the comparison to every material commonly used in electromagnetic shielding, from pure metals to the conductive fabrics used in modern Faraday bags and wearable shielding products.

The physics are straightforward. When an electromagnetic wave hits a conductive surface, two things happen: some energy is reflected (reflection loss) and some energy that enters the material is absorbed as it passes through (absorption loss). Total shielding effectiveness is the sum of both. The specific balance between reflection and absorption depends on the material’s conductivity, its thickness, and the frequency of the incoming signal.

The Comparison Table

Properties that matter for electromagnetic shielding, compared across the most commonly used materials. Conductivity values are relative to copper (IACS — International Annealed Copper Standard), where copper = 100%.

Conductive Fabrics

Modern Faraday bags and wearable shielding rarely use solid metal. They use conductive textiles — woven or knitted fabrics with metal fibers or metal coatings that provide flexibility while maintaining shielding effectiveness.

Frequency-Dependent Performance

No single material provides uniform shielding across the entire electromagnetic spectrum. Shielding effectiveness varies with frequency because the mechanisms — reflection loss and absorption loss — respond differently at different wavelengths.

At lower frequencies (below ~100 MHz), reflection loss dominates for highly conductive materials like copper and aluminum. At higher frequencies (above ~1 GHz), absorption loss becomes more significant, and material thickness relative to skin depth matters more. At millimeter-wave frequencies (24–47 GHz), the very short skin depth means even thin materials can provide substantial absorption — but the very short wavelengths also mean that mesh openings and seam gaps become more critical.

This is why Dispatch #004 emphasized testing across the full frequency range, not just at a single frequency. A product that provides 60 dB attenuation at 1 GHz may provide 30 dB at 6 GHz if it uses a single layer of material optimized for lower frequencies. The modern RF environment spans from 50 Hz to 47 GHz. A shielding product needs to perform across that range — or clearly state which portion it covers.

The Practical Decision

If you’re evaluating shielding materials — for a Faraday bag, a shielded room, or any electromagnetic application — the decision comes down to four variables: frequency range, required attenuation, durability requirements, and budget.

For permanent installations (rooms, enclosures), copper or aluminum sheet provides the best performance at reasonable cost. For flexible consumer products (pouches, bags, cases), multi-layer conductive fabric composites provide the best balance of attenuation, flexibility, and durability. For any application, the closure or seam design matters as much as the material choice — the Faraday cage principle requires a complete enclosure, and the weakest point in any enclosure is the opening.

This dispatch is the reference table. What you build with it is up to you.