What Counts as Foil
Foil is defined by gauge, not by use. In commercial practice aluminium foil is rolled below about 0.2 mm, with the majority of packaging gauges between 6 and 100 micrometres. Household and catering foil typically sits at 10 to 20 micrometres, semi-rigid food container foil at 30 to 90 micrometres, pharmaceutical blister foil at 20 to 30 micrometres, and current-collector foil for lithium-ion cells at 12 to 20 micrometres. EN 546-2 sets mechanical property requirements for foil, while ASTM B479/B479M covers foil for flexible barrier applications.
Alloy choice follows the duty. Aluminium 8011 is the standard Al-Fe-Si household and food-service alloy, with roughly 0.6 to 1.0% iron and 0.5 to 0.9% silicon, which raises strength without hurting formability. Purity grades such as 1235 are used where conductivity or a soft, dead-fold surface matters. Alloy and temper together determine whether the foil dead-folds, springs back, or tears cleanly at a tear-tab line.
The Barrier Advantage
A defect-free aluminium layer is opaque and impermeable to gases, water vapour, light and odours at gauges measured in tens of micrometres. That is the single most important advantage over polymer films, which need multiple layers to approach the same result. Once foil thickness exceeds roughly 9 micrometres, pinholes become rare enough that the water vapour transmission rate falls to a level that is difficult to measure on routine equipment.
| Property | Typical value | Practical consequence |
|---|---|---|
| Density | 2.70 g/cm3 | Low weight per square metre of barrier |
| Thermal conductivity | about 237 W/mK | Fast, even heat transfer in ovens and heat sealers |
| Surface emissivity, bright finish | about 0.03 to 0.05 | Reflective insulation performance |
| Light transmission | zero above 6 to 9 micrometres | Protects fats, vitamins and pharmaceuticals from photo-degradation |
| Working temperature range | deep freeze to oven use | One substrate for the whole cold chain and for baking |
Thermal and Electrical Advantages
Foil spreads heat laterally instead of concentrating it, which is why it gives even browning in ovens, protects delicate edges during grilling, and allows heat sealers to reach a consistent seam temperature across the full web width. The same property serves electrical duty: foil shields against electromagnetic interference, equalises potential across a cable wrap, and acts as a ground plane in laminated boards.
Reflective insulation is the other side of the same coin. With an emissivity near 0.04, a bright foil surface blocks radiant heat transfer, which is why foil-faced board and foil laminates are used behind radiators, in duct wrap and in roof spaces. Performance depends on facing an air gap; foil in direct contact with both surfaces gains far less.
Manufacturing and Cost Advantages
Foil runs on high-speed converting equipment. It can be printed, lacquered, embossed, laminated to paper or polymer film, and dead-folded without a separate forming step, and it converts on standard unwinds and tension systems. Because the functional barrier layer is only a few micrometres thick, the material cost per square metre of barrier is low compared with multi-layer polymer structures of equal performance.
Foil also tolerates the sterilisation and hygiene requirements of medical and pharmaceutical packing. It accepts heat-seal lacquer for blister lids, survives steam sterilisation in laminated form, and provides the light protection required for light-sensitive actives.
Recycling and Life-Cycle Position
Aluminium is recycled without loss of functional quality, and remelt energy is a small fraction of primary production energy. Clean, single-alloy foil trim is a valuable scrap stream, and post-consumer foil is recyclable wherever collection systems accept it. The practical constraint is contamination: foil laminated to paper or plastics is difficult to separate, so mono-material design and clean collection drive the recycling outcome more than the metal itself.
Two design notes follow. First, keep foil gauges as low as the barrier duty allows, because pinhole performance and dead-fold behaviour, not thickness, usually govern the choice. Second, specify the surface finish deliberately: bright rolled surfaces reflect heat best, while matte or lacquered surfaces bond better in lamination and print more reliably.
Frequently Asked Questions
Q: Is aluminium foil a complete barrier to moisture and gases?
A: At gauges above about 9 micrometres, a foil layer is effectively impermeable, provided it is pinhole-free. Below that gauge, pinholes and flex cracking allow measurable transmission, so laminated structures are used.
Q: Why does foil feel hot so quickly in an oven?
A: Aluminium conducts heat at approximately 237 W/mK, far faster than polymer film. Heat reaches the food surface quickly and spreads laterally, reducing hot spots and shortening cooking time.
Q: Which alloy is used for household and food-service foil?
A: Aluminium 8011 is the standard Al-Fe-Si choice, typically with 0.6 to 1.0% iron and 0.5 to 0.9% silicon, which gives useful strength at gauges of 10 to 20 micrometres.
Q: Does foil thickness affect heat sealing?
A: Yes. Heavier gauges need more seal energy and longer dwell to reach seam temperature. Sealing conditions should be re-validated whenever the foil gauge or lacquer system changes.
Q: Is aluminium foil reusable?
A: Clean, uncreased foil can be reused several times for wrapping or covering. Repeated use reduces its flatness, so reflective and sealing performance falls well before the metal itself degrades.
Q: Can foil carry printed branding?
A: Yes. Foil accepts flexographic, gravure and digital print, but the substrate needs a primer or lacquer for ink adhesion, and bright foil changes ink appearance compared with white film.