Yes, aluminum foil blocks RF signals effectively across a wide range of frequencies. Even standard household foil, which is only about 0.016 mm thick, is far thicker than the “skin depth” at which RF energy gets absorbed by aluminum. In practical terms, a single layer of kitchen foil can reduce signal strength by 85 dB or more, which blocks over 99.999% of the energy at common wireless frequencies.
Why Aluminum Blocks RF So Well
When an electromagnetic wave hits a conductive surface like aluminum, the wave’s energy gets absorbed rapidly as it penetrates the metal. The distance it takes for the signal to drop to about 37% of its original strength is called the skin depth. For aluminum, which has very high electrical conductivity, that skin depth is tiny at RF frequencies.
At 680 kHz (AM radio), aluminum’s skin depth is about 0.1 mm. At 108 MHz (FM radio), it shrinks to roughly 0.008 mm, or 8 micrometers. By the time you reach Wi-Fi frequencies like 2.4 GHz and 5 GHz, the skin depth is even smaller. Standard household aluminum foil at 0.016 mm (16 micrometers) is already several skin depths thick at FM frequencies, and many times thicker than the skin depth at Wi-Fi and cellular frequencies. Each additional skin depth reduces the signal by another 63%, so a few skin depths of material eliminates virtually all of the energy passing through.
How Much Signal Gets Blocked
Shielding effectiveness is measured in decibels (dB), where higher numbers mean more signal is blocked. At frequencies between 30 and 100 MHz, aluminum foil provides at least 85 dB of shielding. To put that in perspective, 85 dB means the signal on the other side is reduced to roughly one three-hundred-millionth of its original power. At microwave frequencies like those used by Wi-Fi routers and cell phones, the shielding is even better because the skin depth is smaller relative to the foil’s thickness.
Heavy-duty foil, at about 0.024 mm thick, offers slightly more protection than standard foil, but the difference is marginal for most purposes. A single layer of regular foil is already overkill for blocking Wi-Fi, Bluetooth, cellular, and GPS signals.
Where Foil Shielding Falls Short
The physics of aluminum’s conductivity make it excellent at blocking electric fields and high-frequency electromagnetic waves. But at very low frequencies, particularly from magnetic sources like power lines or transformers, aluminum is much less effective. Low-frequency magnetic fields require materials with high magnetic permeability, like steel or specialized mu-metal, to redirect the field lines. Aluminum doesn’t have that property.
The bigger practical problem isn’t the material itself but gaps and seams. RF signals behave like water finding cracks: any opening, hole, or unsealed seam in your foil lets energy leak through. A perfectly wrapped foil enclosure blocks nearly everything, but a loosely draped sheet with gaps at the edges will let signals in around the sides. For effective shielding, the foil needs to form a continuous conductive barrier with overlapping, tightly sealed joints.
Aluminum Foil vs. Other Shielding Materials
Copper is more conductive than aluminum and provides somewhat higher shielding effectiveness at the same thickness. For professional EMI shielding enclosures, copper is often the gold standard. But aluminum is significantly lighter and cheaper, which is why it’s the preferred material for most real-world shielding applications. The performance gap between the two is small enough that aluminum handles the vast majority of RF blocking tasks just fine.
Thicker aluminum products like expanded sheets and composite panels can achieve shielding values above 90 dB. But for someone wrapping a phone, a key fob, or a router in household foil, the standard product already delivers more attenuation than most situations require.
Common Uses and Practical Tips
People use aluminum foil to block RF signals for a variety of reasons: preventing car key fob relay attacks, testing whether a device is transmitting, blocking Wi-Fi from leaking into certain areas, or shielding sensitive electronics from interference. For all of these, foil works.
If you’re wrapping a device, use at least two layers with overlapping seams to minimize leakage through gaps. Press the foil tightly so there are no air pockets or openings where signals could enter. For key fobs, a tightly wrapped foil pouch will block the low-power signal a relay thief would try to amplify. For blocking Wi-Fi to or from a specific direction, even a flat sheet of foil placed behind a router acts as a reflector, redirecting signal away from that side.
One thing foil won’t do well is create a permanent, reliable enclosure with repeated opening and closing. The material tears easily and doesn’t maintain a good seal over time. For ongoing shielding needs, a commercial Faraday bag or pouch uses conductive fabric that achieves similar results with better durability. But for a quick, cheap test or temporary block, aluminum foil from your kitchen drawer does the job.