Aluminium foil is a rolled product with a thickness below 0.2 mm, produced from high-purity 1xxx alloys and selected 8xxx alloys. Foil for composite structures is normally supplied between 0.006 mm and 0.030 mm, and the metal content of the common barrier grades is high: 1235 foil contains at least 99.35% aluminium, while 8079 foil reaches about 99.8%. Performance is specified in ASTM B479 for flexible barrier and food-contact foil, in EN 546 for European markets and in GB/T 3198, which together cover thickness tolerance, mechanical properties, surface wetting tension and pinhole limits.
Why Aluminum Foil Works as the Barrier Layer
Almost every composite material that needs opacity and a high barrier uses aluminium foil as its barrier layer, and the reason is metallurgical. Foil is a rolled, fully dense metal sheet with a continuous crystal structure and no open porosity, so it blocks gases, water vapour, oxygen, light and micro-organisms by physical exclusion rather than by chemical reaction. No polymer film of the same thickness matches a metal foil for absolute barrier performance, and it tolerates high temperatures and sterilisation.
Foil does have limits. As the gauge falls below roughly 0.009 mm the number of fine pinholes increases and barrier performance drops; the very thin, flexible sheet also has limited resistance to stretching and shear. In practice this is solved by combining the foil with other layers.
Grades and Thickness Selection for Composite Structures
| Alloy | Typical thickness | Aluminium content | Typical use |
|---|---|---|---|
| 1235 | 0.0065-0.009 mm | 99.35% min | General flexible packaging laminates |
| 8079 | 0.006-0.009 mm | About 99.8% | High-barrier food and pharmaceutical laminates |
| 8011 | 0.008-0.030 mm | Al-Fe-Si alloy | Blister foil, closures and semi-rigid packs |
| 1145 | 0.010-0.030 mm | 99.45% min | Building and insulation composites |
How Aluminum Foil Is Combined with Other Materials
Adhesive lamination: foil is bonded to PET, BOPP, paper or nonwoven webs with a polymer adhesive, then cured so the bond survives flexing, retort and ageing.
Extrusion coating: molten polyethylene is extruded between the foil and a sealant or support layer in a single pass.
Coating and varnishing: heat-seal lacquers, print primers and protective varnishes give the laminate sealing and printability.
Online precision compounding and curing: multilayer structures are built by bringing aluminium foil, polymer adhesive and a special PET carrier together, then curing the laminate under a controlled temperature regime so barrier, seal strength and bond strength are achieved in one operation.
The finished structure behaves as one material. The foil supplies absolute barrier and opacity, the polymer layers supply mechanical strength, sealability and print quality, and the adhesive system transfers load between them throughout converting, filling and transport.
Performance Data and Quality Control
Barrier performance is verified on the finished laminate rather than on the foil alone. A structure built around a 0.009 mm foil layer typically delivers a water vapour transmission rate below 0.1 g/m² per 24 h and an oxygen transmission rate below 0.1 cm³/m² per 24 h , so a foil laminate keeps its contents stable for years. Suppliers control pinhole density, thickness tolerance, tensile strength, elongation, wetting tension and adhesion strength, and foil destined for food or pharmaceutical contact must also satisfy the applicable migration and hygiene requirements.
Aluminum Foil in Building Materials
In construction, foil laminates act as long-term guardians against roof leakage and heat loss. Asphalt waterproofing membranes depend on excellent weather resistance, and a foil composite film built from aluminium foil, a polymer adhesive and a special PET carrier blocks water vapour and light. It is used as the surface layer of self-adhesive polymer-modified bituminous waterproofing membranes, where the foil reflects solar radiation and resists ageing.
Frequently Asked Questions
Q: Why is aluminum foil used as the barrier layer in composites?
Because it is a dense rolled metal sheet with a continuous crystal structure, it blocks gas, moisture, light and micro-organisms by physical exclusion, giving barrier performance no polymer film of the same thickness can match.
Q: How thick is the aluminum foil used in laminates?
Foil is defined as material below 0.2 mm thick, but composite and packaging laminates normally use 0.006 mm to 0.030 mm, with 0.0065 mm to 0.009 mm being the most common range.
Q: What purity does composite-grade aluminum foil have?
Barrier grades are made from high-purity alloys: 1235 contains at least 99.35% aluminium and 8079 about 99.8%.
Q: What happens if the foil is made too thin?
Below roughly 0.009 mm the pinhole count rises and barrier performance falls, and the sheet also loses resistance to stretching and shear, so it is always combined with polymer layers to compensate.
Q: Is aluminum foil used on its own?
Rarely. Foil has limited tensile and shear resistance in very thin gauges, so it is laminated or coated with paper, PET, BOPP or polyethylene to build a structure that performs as a single material.
Q: Which standards cover aluminum foil?
ASTM B479 governs flexible barrier and food-contact foil, EN 546 covers foil supplied in Europe, and GB/T 3198 specifies aluminium and aluminium alloy foils for the Chinese market.
