Definition
A very thin, flexible sheet of metal, typically rolled or hammered to a thickness of less than 0.006 inch. In aviation, metal foils are used for shimming, shielding, decorative trim, capacitor plates, and as a backing material in some bonded structures and gaskets.
Plain English
A paper-thin sheet of metal. Thin enough to bend easily with your fingers, but still solid metal — not a coating or a film.
Context Anchor
Seen in aircraft maintenance and materials discussions when identifying thin metal stock by thickness.
Derivation
Foil comes from the Latin folium, meaning leaf. The word captures the idea well — metal rolled so thin it behaves almost like a leaf, easily folded or wrapped.
Why Pilots Care
A pilot may see this term in maintenance records or aircraft material descriptions. Knowing that foil is a thickness category helps avoid confusing it with stronger, thicker sheet metal used for structural parts.
Analogy
It is similar in thinness to household aluminum foil, but aircraft metal foil is specified by its exact metal type and thickness, not by kitchen use.
Intuition Check
Do not read “foil” here as an airfoil or only as kitchen aluminum foil. In this context, metal foil means any metal rolled into a very thin layer, usually defined by thickness.
Example Sentence 1
The technician used a thin strip of metal foil as a shim to bring the bracket into proper alignment.
Example Sentence 2
Inspectors checked the metal foil layer for damage after the aircraft took a lightning strike on the ramp.