Foil conducts electricity because it is made from aluminum, a highly conductive metal. Common household aluminum foil is simply a thin sheet of this metal, which retains the material’s inherent ability to allow electric charge to flow freely. This property remains regardless of how thinly the material is rolled.
The Material Science Behind Foil’s Conductivity
Aluminum is a metal, and all metals share a unique atomic structure that explains their high electrical conductivity. In solid aluminum, the atoms are arranged in a rigid, crystalline lattice structure. The outermost electrons, known as valence electrons, are not tightly bound to a single atom.
These valence electrons become delocalized, forming a “sea of electrons” that moves throughout the metallic lattice. The mobility of these free electrons allows for the easy movement of electric charge. When a voltage is applied, these mobile electrons are pushed from one end of the foil to the other, creating an electric current.
Aluminum is an excellent conductor, ranking as the fourth-best electrical conductor among all metals, following silver, copper, and gold. Its conductivity is approximately 61% of copper’s, which is why aluminum is widely used in electrical transmission lines.
Safety Risks and Electrical Hazards
Because aluminum foil is a good conductor, using it improperly near electrical sources creates serious safety risks. The danger lies in the foil’s high conductivity combined with its extremely thin structure.
When foil bridges two points in an electrical circuit, it creates a short circuit, allowing a massive surge of current to flow. Although the foil offers little resistance, the current flow is so high that it causes rapid heating, a process known as Joule heating. The thin metal cannot dissipate this heat quickly enough and can reach its melting point of about 660°C almost instantly.
This rapid heating poses a severe fire hazard, especially when the foil is placed near flammable materials. For example, placing crumpled foil in a microwave oven can cause arcing and sparking because the sharp points concentrate the electric field. Using foil to repair a broken fuse or to bridge a battery terminal is highly dangerous, as it can cause the battery to overheat or the circuit to overload.
Intentional Uses for Electrical Shielding
The high electrical conductivity of aluminum foil is intentionally leveraged in many technical and commercial applications, particularly for protection against electromagnetic interference (EMI). Aluminum foil acts as a shield by reflecting and absorbing electromagnetic waves, a direct consequence of its metallic structure.
When an electromagnetic wave encounters the conductive surface of the foil, the free electrons within the metal rapidly rearrange themselves to cancel out the incoming field. This reflection mechanism is effective, with aluminum foil capable of reflecting over 88% of incident electromagnetic waves in certain frequency ranges. Technicians often use foil to create a temporary Faraday cage, an enclosure that blocks external electric fields.
This shielding property is used extensively in electronics, such as wrapping bundles of sensitive wiring to prevent signal disruption from nearby power cables. Aluminum foil is also used in the manufacturing of various cables, where it is wrapped around the inner conductors to maintain signal integrity. Conductive aluminum foil is also used in some touch sensor circuits to shield them from external noise that could cause functional errors.