What Aluminized Packaging Actually Is
Aluminized, or metallized, packaging is a polymer film carrying a thin vacuum-deposited aluminium layer rather than a solid foil. The layer is produced by evaporating high-purity aluminium in a vacuum chamber and condensing it onto a moving web, giving a coating of about 30-60 nm - roughly one two-hundredth of the thickness of a 9 micrometre foil. The coating is specified by optical density, normally 2.0-2.5, which corresponds to light transmission below 1% and produces both the silver appearance and the barrier improvement that the market pays for. Base films are usually 12 micrometre PET, 20-25 micrometre OPP or cast PP, which are then laminated, printed or coated.
How the Market Developed
Metallized film entered packaging in the 1960s and expanded quickly in North America and Europe during the 1980s, once vacuum coating lines reached the widths and speeds that made the process cheaper than foil lamination. Adoption came in three waves: decorative and security labels first, then outer and flexible packaging, then cigarette lining paper and specialised laminates. The driving force has been economic rather than purely technical, because a metallized layer consumes a fraction of the aluminium needed for solid foil, so material cost falls while the visual effect stays close to foil. Where barrier requirements are moderate, metallized structures have replaced foil laminates; where the specification demands an absolute barrier, foil still wins.
Barrier Performance and How It Is Measured
Barrier is reported as water vapour transmission rate (WVTR) and oxygen transmission rate (OTR), measured to ASTM F1249 for moisture and ASTM D3985 for oxygen. Test conditions for WVTR are normally 38 C and 90% relative humidity, and results must always be quoted with the conditions used.
| Structure | Aluminium layer (nm) | WVTR (g/m2 per 24 h) | OTR (cm3/m2 per 24 h) |
|---|---|---|---|
| Uncoated 12 micrometre PET | none | 15-25 | 80-120 |
| Metallized 12 micrometre PET | 40-60 | 0.3-1.0 | 0.5-1.5 |
| Metallized 25 micrometre OPP | 40-60 | 0.3-1.0 | 15-40 |
| PET / 9 micrometre foil / PE laminate | 9000 | below 0.01 | below 0.01 |
Two practical conclusions follow. First, metallization improves barrier by one to two orders of magnitude over an uncoated polymer, but remains far behind a foil laminate because pinholes and coating defects allow slow diffusion. Second, the achieved barrier depends on substrate and handling: flexing, creasing and even printing raise transmission rates, so converters should specify barrier on the finished laminate rather than on the film.
Cost, Regulatory and Recycling Considerations
Food contact compliance is assessed against EU 1935/2004 and, for the United States, 21 CFR 175.300 for resinous coatings; migration testing on the finished article remains the packer's responsibility, and the aluminium layer itself should meet the purity expectations of EN 602 for wrought aluminium in contact with food. Because the metal layer is so thin, a mono-material design such as metallized PET laminated to PE is easier to place in a recycling stream than a foil/polymer laminate, and the metal content does not disturb most mechanical recycling processes. Cost per square metre is typically a fraction of an equivalent foil structure, but the saving must be set against the higher WVTR when the product is moisture sensitive.
Specifying Metallized Film for a Purchase Order
A complete specification names the substrate and gauge, aluminium optical density, coating adhesion, seal side, wound direction, core diameter, roll width, maximum splice count per roll and shelf life. Barrier data should be requested on the laminated structure at stated test conditions, together with blocking and coefficient of friction values for the converting line. For high-humidity or long shelf life products, the metallized film should be treated as one layer of a designed laminate rather than as a stand-alone barrier.
Frequently Asked Questions
Q: Can metallized film replace aluminium foil completely?
A: Only where barrier requirements are moderate. Metallized film reaches WVTR in the 0.3-1.0 g/m2 per 24 h range, while a 9 micrometre foil laminate holds below 0.01, so moisture-sensitive or long-life products still need foil.
Q: What optical density should be specified?
A: 2.0-2.5 for packaging. Below 2.0 the coating becomes visibly translucent and barrier drops; above 2.5 the extra aluminium adds cost without measurable barrier gain.
Q: Which side of the film is metallized?
A: The coating is always applied to one face. In laminating, the metallized surface is usually buried inside the laminate so that the coating is protected from abrasion and from direct contact with the product.
Q: Does printing damage the barrier?
A: Printing, especially with solvent based inks and hot drying, can raise WVTR. Barrier should be verified on the printed or laminated structure, not on plain metallized film.
Q: How is coating adhesion tested?
A: Normally by tape adhesion or rub tests agreed between buyer and supplier, since the vacuum coating is thin and adhesion depends on surface treatment of the base film.
Q: Is aluminized film suitable for food contact?
A: Yes, when the construction complies with EU 1935/2004 and the relevant national rules, with migration testing carried out on the finished article.