What Makes a Rolled Product "Foil"
Aluminium foil is a rolled product supplied at a thickness below 0.2 mm, normally in coil form and usually produced from 1xxx, 3xxx and 8xxx alloys. Foil is not simply thin sheet. Once the gauge falls below roughly 0.05 mm the material is rolled in a pack, with two sheets passing through the mill together and then separated, which leaves one bright side and one matte side. That double-rolling step is the practical boundary between foil and light-gauge sheet.
Because packaging foil contains more than 99% aluminium, its physical behaviour is governed mainly by thickness, temper and surface condition rather than by alloying additions. Trace iron and silicon levels still matter, however, since they control recrystallisation, grain size and the strength that survives a soft anneal.
Key Physical Properties at a Glance
Density: 2.70 to 2.71 g/cm3 for 1xxx and 8xxx packaging alloys
Melting range: approximately 646 to 660 °C for commercially pure aluminium
Thermal conductivity: about 235 W/(m·K) at 20 °C in the annealed state
Electrical conductivity: roughly 61% IACS when fully annealed, lower in harder tempers
Light reflectance: 75 to 88% on the bright side, depending on rolling finish
Thermal emittance: below 0.05 for a clean bright surface, rising as the surface oxidises
Modulus of elasticity: about 69 GPa
Specific gravity effect: approximately one third the density of steel or copper
Barrier behaviour: fully opaque to visible light and an effective water-vapour barrier when free of pinholes
Thickness, Temper and Indicative Property Data
Packaging foil starts at 0.006 mm and extends to about 0.2 mm. Lidding, laminating and insulation grades commonly sit between 0.007 mm and 0.05 mm. Mechanical response follows the temper state: soft O-temper material is chosen where elongation and dead-fold behaviour matter, while H18 and H19 tempers deliver much higher tensile strength with almost no remaining elongation. The ranges below are indicative, chosen to show how temper shifts the balance between strength and ductility; the applicable delivery standard governs actual acceptance.
| Grade and temper | Thickness range | Tensile strength | Elongation | Typical use |
|---|---|---|---|---|
| 1235-O | 0.006 to 0.020 mm | 45 to 75 MPa | 15% and above | Household wrap, laminating foil |
| 8079-O | 0.007 to 0.030 mm | 50 to 85 MPa | 12% and above | Converter foil for flexible laminates |
| 8011-O | 0.009 to 0.100 mm | 85 to 125 MPa | 15% and above | Pharmaceutical and container foil |
| 8011-H18 | 0.009 to 0.100 mm | 150 to 200 MPa | 1 to 4% | Lidding stock requiring stiffness |
| 1100-O | 0.025 to 0.200 mm | 75 to 110 MPa | 20% and above | Insulation, heat exchange, ducting |
| 3003-H24 | 0.030 to 0.200 mm | 130 to 180 MPa | 3 to 10% | Semi-rigid trays and containers |
Gauge tolerance is expressed as a percentage of nominal thickness and tightens as the foil becomes thinner, which is why thickness profile and pinhole count are the two measurements most often quoted on inspection certificates. GB/T 3198 covers aluminium and aluminium alloy foil for general use, EN 546-1 sets out the classification and delivery conditions for European foil, and ASTM B479 addresses annealed aluminium foil intended for flexible barrier applications.
Barrier, Optical and Thermal Behaviour
A pinhole-free foil of about 0.009 mm is effectively impermeable, with water-vapour transmission measured by ASTM E96 typically below 0.01 g per square metre over 24 hours. Barrier quality is therefore a function of pinhole density rather than of alloy: as gauge falls, the probability of pinholes and of crease-related cracks rises sharply, and a single fold can open a continuous leak path across the sheet.
Optically the metal is a mirror. Visible light is reflected rather than transmitted, and in the infrared the same surface both reflects radiant heat and re-emits very little, which is the property exploited in insulation facings and in heat shields. The natural oxide layer that forms within seconds of rolling is only 2 to 4 nm thick and is self-limiting, so it provides mild passivation without altering the reflective behaviour. It is not, however, sufficient protection in wet contact with steel or with alkaline building materials, where galvanic or chemical attack can occur.
Electrically, annealed foil carries roughly 61% of the conductivity of copper while weighing about half as much for the same volume, which is why thin foil is used in cable shielding and in winding applications where weight is critical. Thermal expansion is about 23 × 10-6 per °C, close to that of many polymers, so laminates of foil and film generally remain dimensionally compatible over normal service temperatures.
Selection, Handling and Conversion Notes
Choose temper against the forming operation: deep drawing and folding need the elongation of an O temper, while a flat lidding membrane benefits from H18 stiffness.
Unsupported foil below about 0.02 mm is handled as a pack or on a liner; tension and web speed on the laminating line have more influence on breakage than alloy choice.
Dead-fold retention improves with soft temper and is important for hand wrapping, but it also means creases cannot be avoided in handling.
Store coils dry and below about 40 °C. Moisture condensation between laps produces staining and can promote surface corrosion.
Bare foil will darken if it is exposed to humid or acidic air for long periods; decorative and hot-stamping uses therefore rely on a lacquer or a laminate to hold the appearance.
Verify wettability and residual rolling-oil level before printing or coating, since these properties decide whether adhesives and inks will bond reliably.
Frequently Asked Questions
Q: What is the density of aluminium foil?
About 2.70 to 2.71 g/cm3 for the 1xxx and 8xxx alloys used in packaging and insulation, which is roughly one third the density of steel or copper.
Q: Why does foil have a bright side and a matte side?
Because gauges below about 0.05 mm are rolled as a pack of two sheets. The surface in contact with the mill rolls is bright, while the inner faces rub against each other and become matte.
Q: How thin can aluminium foil be produced?
Volume production currently reaches 0.006 mm, which is less than one tenth the diameter of a human hair. Thinner gauges are possible in limited widths but become fragile during packing and converting.
Q: Is foil a complete barrier against moisture and oxygen?
Yes, provided it is pinhole-free. Barrier performance is limited by pinhole density and by creases, so the effective barrier depends on gauge, handling and the supporting film in a laminate.
Q: Over what temperature range can foil be used?
Uncoated foil tolerates roughly -200 °C to +300 °C. Where an organic coating or a polymer laminate is applied, the coating normally sets the practical upper limit, often near 200 °C.
Q: Does the natural oxide film protect the foil from corrosion?
It slows attack in ordinary air because the 2 to 4 nm layer is dense and self-limiting, but it does not prevent galvanic corrosion in wet contact with steel or attack by strong alkalis.
Q: Which standards apply to aluminium foil properties?
GB/T 3198 covers general foil, EN 546-1 covers European classification and delivery conditions, ASTM B479 covers annealed foil for flexible barrier use, and ASTM E96 is used for water-vapour transmission testing.
